Analysis of vitamin D metabolic markers by mass spectrometry: current techniques, limitations of the "gold standard" method, and anticipated future directions

Vitamin D compounds belong to a group of secosteroids, which occur naturally as vitamin D3 in mammals and D2 in plants. Vitamin D is vital for bone health but recent studies have shown a much wider role in the pathologies of diseases such as diabetes, cancer, autoimmune, neurodegenerative, mental and cardiovascular diseases. Photosynthesis of vitamin D in the human skin and subsequent hepatic and renal metabolism generate a wide range of transformation products occurring over a large dynamic range spanning from picomolar to nanomolar levels. This necessitates selective and sensitive analytical methods to quantitatively capture these low concentration levels in relevant tissues such as blood. Ideally, vitamin D assessment would be performed using a universal and standardized analytical method available to clinical laboratories that provides reliable and accurate quantitative results for all relevant vitamin D metabolites with sufficiently high throughput. At present, LC-MS/MS assays are the most promising techniques for vitamin D analysis. The present review focuses on developments in mass spectrometry methodologies of the past 12 years. It will highlight detrimental influences of the biological matrix, epimer contributions, pitfalls of specific mass spectrometry data acquisition routines (in particular multiple reaction monitoring, MRM), influence of ionization source, derivatization reactions, inter-laboratory comparisons on precision, accuracy, and application range of vitamin D metabolites.

Blood spot-based measures of glucose homeostasis and diabetes prevalence in a nationally representative population of young US adults

PURPOSE

We investigated understudied biomarker-based diabetes among young US adults, traditionally characterized by low cardiovascular disease risk.

METHODS

We examined 15,701 participants aged 24 to 32 years at Wave IV of the National Longitudinal Study of Adolescent Health (Add Health, 2008). The study used innovative and relatively noninvasive methods to collect capillary whole blood via finger prick at in-home examinations in all 50 states.

RESULTS

Assays of dried blood spots produced reliable and accurate values of HbA1c. Reliability was lower for fasting glucose and lowest for random glucose. Mean (SD) HbA1c was 5.6% (0.8%). More than a quarter (27.4%) had HbA1c-defined prediabetes. HbA1c was highest in the black, non-Hispanic race/ethnic group, inversely associated with education, and more common among the overweight/obese and physically inactive. The prevalence of diabetes defined by previous diagnosis or use of antidiabetic medication was 2.9%. Further incorporating HbA1c and glucose values, the prevalence increased to 6.8%, and among these participants, 38.9% had a previous diagnosis of diabetes (i.e., aware). Among those aware, 37.6% were treated and 64.0% were controlled (i.e., HbA1c < 7%).

CONCLUSIONS

A contemporary cohort of young adults faces a historically high risk of diabetes but there is ample opportunity for early detection and intervention.

Automated high-capacity on-line extraction and bioanalysis of dried blood spot samples using liquid chromatography/high-resolution accurate mass spectrometry

RATIONALE

Pharmacokinetic data to support clinical development of pharmaceuticals are routinely obtained from liquid plasma samples. The plasma samples require frozen shipment and storage and are extracted off-line from the liquid chromatography/tandem mass spectrometry (LC/MS/MS) systems. In contrast, the use of dried blood spot (DBS) sampling is an attractive alternative in part due to its benefits in microsampling as well as simpler sample storage and transport. However, from a practical aspect, sample extraction from DBS cards can be challenging as currently performed. The goal of this report was to integrate automated serial extraction of large numbers of DBS cards with on-line liquid chromatography/high-resolution accurate mass spectrometry (LC/HRAMS) bioanalysis.

METHODS

An automated system for direct DBS extraction coupled to a LC/HRAMS was employed for the quantification of midazolam (MDZ) and α-hydroxymidazolam (α-OHMDZ) in human blood. The target analytes were directly extracted from the DBS cards onto an on-line chromatographic guard column followed by HRAMS detection. No additional sample treatment was required. The automated DBS LC/HRAMS method was developed and validated, based on the measurement at the accurate mass-to-charge ratio of the target analytes to ensure specificity for the assay.

RESULTS

The automated DBS LC/HRAMS method analyzed a DBS sample within 2 min without the need for punching or additional off-line sample treatment. The fully automated analytical method was shown to be sensitive and selective over the concentration range of 5 to 2000 ng/mL. Intra- and inter-day precision and accuracy was less than 15% (less than 20% at the LLOQ). The validated method was successfully applied to measure MDZ and α-OHMDZ in an incurred human sample after a single 7.5 mg dose of MDZ.

CONCLUSIONS

The direct DBS LC/HRAMS method demonstrated successful implementation of automated DBS extraction and bioanalysis for MDZ and α-OHMDZ. This approach has the potential to promote workload reduction and sample throughput increase.

Therapeutic drug monitoring by dried blood spot: progress to date and future directions

This article discusses dried blood spot (DBS) sampling in therapeutic drug monitoring (TDM). The most important advantages of DBS sampling in TDM are the minimally invasive procedure of a finger prick (home sampling), the small volume (children), and the stability of the analyte. Many assays in DBS have been reported in the literature over the previous 5 years. These assays and their analytical techniques are reviewed here. Factors that may influence the accuracy and reproducibility of DBS methods are also discussed. Important issues are the correlation with plasma/serum concentrations and the influence of hematocrit on spot size and recovery. The different substrate materials are considered. DBS sampling can be a valid alternative to conventional venous sampling. However, patient correlation studies are indispensable to prove this. Promising developments are dried plasma spots using membrane and hematocrit correction using the potassium concentration.

Dried blood spot testing for the antenatal screening of HTLV, HIV, syphilis, toxoplasmosis and hepatitis B and C: prevalence, accuracy and operational aspects

INTRODUCTION

Screening for vertically transmitted infection is mandatory and must be conducted at the first prenatal consultation. The most vulnerable women's groups are those at the lowest socio-economic level. Dried blood spot testing on filter paper could represent a secure way to screen pregnant women in the prenatal period.

METHODS

A cross-sectional study was conducted between November 2009 and March 2010, in the Metropolitan Region of Salvador, Bahia, Brazil, to compare the accuracy of the dried blood spot in filter paper and venipuncture serological as screening methods for HIV, HTLV, VHB, VHC, Treponema pallidum, and Toxoplasma gondii during prenatal period. Results of the venous blood sample collected in tubes were considered the gold standard.

RESULTS

Serum samples and dried blood spot were obtained from 692 pregnant women aged between 14 and 42 years, with a median age of 26. Thirteen women were seropositive for T. gondii (1.88%; 95% CI: 0.60-2.71%), five for T. pallidum (0.72%; 95% CI: 0.15-1.61%), two for HBV (0.29%; 95% CI: 0.050.95%) and one for HTLV-1 (0.14%; 95% CI: 0.01-0.71%). No one was positive for HCV and HIV. The dried blood spot accuracy for syphilis and HTLV were 100% (95% CI: 99.25-100) and 100% (95% CI: 99.45-100%), respectively. The average time between blood collection and recording of the sample in the reference laboratory was 4.93 (3.82) days and between dried blood spot processing and active search for pregnant women was 3.44 (4.27) days.

CONCLUSIONS

The use of dried blood spot may represent a secure way to expedite access to results of vertically transmitted diseases in the prenatal period, particularly in regions with scarce healthcare resources.

Dried fluid spots for peste des petits ruminants virus load evaluation allowing for non-invasive diagnosis and genotyping

BACKGROUND

Active surveillance of peste des petits ruminants (PPR) should ease prevention and control of this disease widely present across Africa, Middle East, central and southern Asia. PPR is now present in Turkey at the gateway to the European Union. In Bangladesh, the diagnosis and genotyping of PPR virus (PPRV) may be hampered by inadequate infrastructures and by lack of proper clinical material, which is often not preserved under cold chain up to laboratories. It has been shown previously that Whatman® 3MM filter paper (GE Healthcare, France) preserves the nucleic acid of PPRV for at least 3 months at 32°C.

RESULTS

In this study, we demonstrate the performances of filter papers for archiving RNA from local PPRV field isolates for further molecular detection and genotyping of PPRV, at -70°C combined with ambient temperature, for periods up to 16 months. PPR-suspected live animals were sampled and their blood and nasal swabs were applied on filter papers then air dried. Immediately after field sampling, RT-PCR amplifying a 448-bp fragment of the F gene appeared positive for both blood and nasal swabs when animals were in febrile stage and only nasal swabs were detected positive in non-febrile stage. Those tested positive were monitored by RT-PCR up to 10 months by storage at -70°C. At 16 months, using real time RT-PCR adapted to amplify the N gene from filter paper, high viral loads could still be detected (~2 x 10(7) copy numbers), essentially from nasal samples. The material was successfully sequenced and a Bayesian phylogenetic reconstruction achieved adequate resolution to establish temporal relationships within or between the geographical clusters of the PPRV strains.

CONCLUSIONS

This clearly reveals the excellent capacity of filter papers to store genetic material that can be sampled using a non-invasive approach.

Evaluation of dried blood spots collected on filter papers from three manufacturers stored at ambient temperature for application in HIV-1 drug resistance monitoring

As more HIV-infected people gain access to antiretroviral therapy (ART), monitoring HIV drug resistance (HIVDR) becomes essential to combat both acquired and transmitted HIVDR. Studies have demonstrated dried blood spots (DBS) are a suitable alternative in HIVDR monitoring using DBS collected on Whatman 903 (W-903). In this study, we sought to evaluate two other commercially available filter papers, Ahlstrom 226 (A-226) and Munktell TFN (M-TFN), for HIVDR genotyping following ambient temperature storage. DBS were prepared from remnant blood specimens collected from 334 ART patients and stored at ambient temperature for a median time of 30 days. HIV-1 viral load was determined using NucliSENS EasyQ® HIV-1 v2.0 RUO test kits prior to genotyping of the protease and reverse transcriptase regions of the HIV-1 pol gene using an in-house assay. Among the DBS tested, 26 specimens had a viral load ≥1000 copies/mL in all three types of filter paper and were included in the genotyping analysis. Genotyping efficiencies were similar between DBS collected on W-903 (92.3%), A-226 (88.5%), and M-TFN (92.3%) filter papers (P = 1.00). We identified 50 DR-associated mutations in DBS collected on W-903, 33 in DBS collected on A-226, and 48 in DBS collected on M-TFN, resulting in mutation detection sensitivities of 66.0% for A-226 and 88.0% for M-TFN when compared to W-903. Our data indicate that differences among filter papers may exist at this storage condition and warrant further studies evaluating filter paper type for HIVDR monitoring.

Development of an assay to simultaneously measure orotic acid, amino acids, and acylcarnitines in dried blood spots

BACKGROUND

Orotic aciduria in the presence of hyperammonemia is a key indicator for a defect in the urea cycle, specifically ornithine transcarbamylase (OTC) deficiency. Current newborn screening (NBS) protocols can detect several defects of the urea cycle, but screening for OTC deficiency remains a challenge due to the lack of a suitable assay. The purpose of this study was to develop a high-throughput assay to measure orotic acid in dried blood spot (DBS) specimens as an indicator for urea cycle dysfunction, which can be readily incorporated into routine NBS.

METHODS

Orotic acid was extracted from DBS punches and analyzed using flow-injection analysis tandem mass spectrometry (FIA-MS/MS) with negative-mode ionization, requiring <2 min/sample run time. This method was then multiplexed into a conventional newborn screening assay for analysis of amino acids, acylcarnitines, and orotic acid.

RESULTS

We describe 2 assays which can quantify orotic acid in DBS: a stand-alone method and a combined method for analysis of orotic acid, amino acids, and acylcarnitines. Both methods demonstrated orotic acid recovery of 75-85% at multiple levels of enrichment. Precision was also comparable to traditional FIA-MS/MS methods. Analysis of residual presumptively normal NBS specimens demonstrated a 5:1 signal to noise ratio and the average concentration of orotic acid was approximately 1.2 μmol/l. The concentration of amino acids and acylcarnitines as measured by the combined method showed no significant differences when compared to the conventional newborn screening assay. In addition, retrospective analysis of confirmed patients and presumptively normal newborn screening specimens suggests potential for the methods to identify patients with OTC deficiency, as well as other urea cycle defects.

CONCLUSION

The assays described here quantify orotic acid in DBS using a simple extraction and FIA-MS/MS analysis procedures that can be implemented into current NBS protocols.

Comparative evaluation of newborn bloodspot specimen cards by experienced laboratory personnel and by an optical scanning instrument

A major factor in determining the suitability of a dried blood spot (DBS) specimen is the subjective nature of evaluation by laboratory personnel. Using newborn screening DBS specimen cards as they were submitted to a public health NBS program, we conducted a systematic pilot study of DBS evaluation by multiple experienced laboratory personnel (ELP) and by an automated optical scanning instrument (OSI) (CardScan (tm), BSD Robotics). OSI confirmed the satisfactory status of all newborn DBS specimen cards that passed initial review by the first ELP. Among the questionable cards selected for further review, 58% passed multiple ELP consensus assessment, and 62% passed OSI evaluation. The overall agreement between ELP and OSI was 86%. Among questionable specimen cards, ELP and OSI were more strongly correlated when multiple ELP assessment was unanimous. We conclude that subjective assessment by ELP is essential and that OSI evaluation is a useful adjunct when ELP assessment does not reach consensus. OSI further allows the selection of optimal locations for punching DBS from unsatisfactory or questionable specimens, optimizing the quality of interim analyses that may be conducted while repeat specimens are being collected. Instrument evaluation of specimen cards would also be valuable as an independent reference method for training laboratory and specimen collection personnel. OSI technology merits further studies to confirm and extend our findings.

Measurements of 25-hydroxyvitamin D concentrations in archived dried blood spots are reliable and accurately reflect those in plasma

CONTEXT

Recognition that vitamin D might be associated with many chronic diseases has led to large-scale epidemiological and clinical studies. Dried blood spots (DBS) are a useful resource for these studies. Consequently, accurate, efficient, and inexpensive assays to quantify 25-hydroxyvitamin D (25OHD) in DBS are required.

OBJECTIVE

This study evaluated the validity and reliability of a liquid chromatography-tandem mass spectrometry assay for measuring 25OHD in archived DBS and compared measurements of 25OHD in DBS with those in plasma.

DESIGN AND PARTICIPANTS

Sixty-two participants in the Melbourne Collaborative Cohort Study who had plasma and matching DBS stored since study entry in the early 1990s were randomly selected for a study calibrating 25OHD concentrations in DBS with plasma. As part of a study of vitamin D and mortality, cancer, and diabetes, we also assessed the reliability of measurements from DBS using 500 replicates placed randomly within 31 batches run over 15 months.

OUTCOME MEASURE

25OHD concentrations were measured by liquid chromatography-tandem mass spectrometry.

RESULTS

There was good agreement between measurements of 25OHD from DBS and plasma; R(2) = 0.73 from a regression of plasma concentration on DBS concentration. The within-batch and between-batch intraclass correlations from the 500 replicate measurements were 0.82 (95% confidence interval, 0.80, 0.85) and 0.73 (95% confidence interval, 0.68, 0.78), respectively.

CONCLUSIONS

Measuring 25OHD in DBS is a valid and reliable alternative to measuring 25OHD in sera or plasma. A simple calibration model was developed to convert measurements from DBS to equivalent plasma measurements, thus enabling comparisons against clinical reference ranges and with studies using sera or plasma samples.

A practical method to measure GFR in people with type 1 diabetes

AIMS

Improved early diagnostic methods are needed to identify risk for kidney disease in people with type 1 diabetes. We hypothesized that glomerular filtration rate (GFR) measured by iohexol clearance in dried blood spots (DBS) on filter paper would be comparable to plasma (gold-standard) and superior to estimated GFR (eGFR) and, second, that adjustment for ambient blood glucose would improve accuracy and precision of GFR measurement.

METHODS

GFR was measured by iohexol clearance in plasma, DBS, and as estimated by the CKD-Epidemiology Collaboration equations in 15 adults with type 1 diabetes at two visits, one euglycemic and one hyperglycemic.

RESULTS

GFR measured by DBS was more comparable and less biased than GFR cystatin C, serum creatinine, and both combined. GFR was higher during hyperglycemia. Correction for between visit glycemia statistically significantly reduced bias and mean squared error for GFR measured by DBS as compared to gold-standard during euglycemia.

CONCLUSIONS

Iohexol clearance measured with DBS performed better than eGFR methods. Correction for ambient blood glucose improved precision and accuracy of GFR measurement. This method is more convenient than the gold-standard GFR method and may improve screening and diagnostic capabilities in people with type 1 diabetes, especially when GFR is >60ml/min/1.73m(2).

Succinylacetone as primary marker to detect tyrosinemia type I in newborns and its measurement by newborn screening programs

Tyrosinemia type I (TYR I) is caused by autosomal recessive fumarylacetoacetate hydrolase deficiency and is characterized by development of severe liver disease in infancy and neurologic crises. If left untreated, most patients die of liver failure in the first years of life. Intervention with medication is effective when initiated during the first month of life. This improvement in the treatment of TYR I patients influenced the decision to include TYR I in the US Secretary of the Department of Health and Human Services' (HHS) Recommended Uniform Screening Panel. However, while tyrosine is routinely measured in newborn screening (NBS) by tandem mass spectrometry (MS/MS), elevated tyrosine levels are not specific to TYR I. To improve the specificity of NBS for TYR I, several assays were developed to measure succinylacetone (SUAC) in dried blood spots (DBS). SUAC is a pathognomonic marker of TYR I, and its detection by NBS MS/MS is possible. This review of the current status of NBS for TYR I in the US is the result of discussions at the HHS Secretary's (Discretionary) Advisory Committee on Heritable Disorders in Newborns and Children about the inconsistent implementation of effective NBS for TYR I in the US. We sought to understand the different TYR I screening practices in US NBS programs. Results indicate that 50 out of 51 NBS programs in the US screen for TYR I, and a successful SUAC performance evaluation scheme is available from the Centers for Disease Control and Prevention. Programmatic and methodological barriers were identified that prevent widespread adoption of SUAC measurements in NBS laboratories. However, since SUAC detection is currently the best approach to NBS for TYR I, a further delay of the addition of SUAC measurement into NBS procedures is discouraged. SUAC measurement should improve both the false positive and false negative rate in NBS for TYR I thereby yielding the desired benefits for affected patients at no expense to the overall population served.

Novel heparan sulfate assay by using automated high-throughput mass spectrometry: Application to monitoring and screening for mucopolysaccharidoses

Mucopolysaccharidoses (MPS) are caused by deficiency of one of a group of specific lysosomal enzymes, resulting in excessive accumulation of glycosaminoglycans (GAGs). We previously developed GAG assay methods using liquid chromatography tandem mass spectrometry (LC-MS/MS); however, it takes 4-5 min per sample for analysis. For the large numbers of samples in a screening program, a more rapid process is desirable. The automated high-throughput mass spectrometry (HT-MS/MS) system (RapidFire) integrates a solid phase extraction robot to concentrate and desalt samples prior to direction into the MS/MS without chromatographic separation; thereby allowing each sample to be processed within 10s (enabling screening of more than one million samples per year). The aim of this study was to develop a higher throughput system to assay heparan sulfate (HS) using HT-MS/MS, and to compare its reproducibility, sensitivity and specificity with conventional LC-MS/MS. HS levels were measured in the blood (plasma and serum) from control subjects and patients with MPS II, III, or IV and in dried blood spots (DBS) from newborn controls and patients with MPS I, II, or III. Results obtained from HT-MS/MS showed 1) that there was a strong correlation of levels of disaccharides derived from HS in the blood, between those calculated using conventional LC-MS/MS and HT-MS/MS, 2) that levels of HS in the blood were significantly elevated in patients with MPS II and III, but not in MPS IVA, 3) that the level of HS in patients with a severe form of MPS II was higher than that in an attenuated form, 4) that reduction of blood HS level was observed in MPS II patients treated with enzyme replacement therapy or hematopoietic stem cell transplantation, and 5) that levels of HS in newborn DBS were elevated in patients with MPS I, II or III, compared to those of control newborns. In conclusion, HT-MS/MS provides much higher throughput than LC-MS/MS-based methods with similar sensitivity and specificity in an HS assay, indicating that HT-MS/MS may be feasible for diagnosis, monitoring, and newborn screening of MPS.

Simultaneous determination of cystathionine, total homocysteine, and methionine in dried blood spots by liquid chromatography/tandem mass spectrometry and its utility for the management of patients with homocystinuria

BACKGROUND

Disorders of homocysteine and B-vitamin metabolism represent a significant problem in clinical practice. Establishing the diagnosis requires specialized tests with demanding preanalytical requirements. To advance the detection of patients with these disorders, we developed a method for the simultaneous determination of cystathionine (Cysta), methionine (Met) and total homocysteine (tHcy) in dried blood spots (DBSs).

METHODS

A punch from a DBS sample was mixed with a solution of isotopically labeled internal standards, and analytes were extracted using methanol/0.1% formic acid/0.5mol/L dithiothreitol. The extract was injected into an LC-MS/MS system operating in MRM mode.

RESULTS

The analytical performance of the method employing DBS is adequate for its purpose and the type of sample. Compared with Cysta, tHcy and Met plasma levels, our method exhibited a negative bias between -3.8% and -42.2% due to the lower concentrations of these analytes in erythrocytes. The tHcy level and the Met/Cysta ratio in DBS enabled the clear detection of 12 patients with disorders of transsulfuration and with genetic and nutritional remethylation defects.

CONCLUSIONS

The ease of collecting and transporting DBS samples may advance diagnostic procedures in patients with neuropsychiatric disorders and thromboembolism. Consequently, this approach may facilitate detection and simplify the monitoring of patients with homocystinuria.

Comparison of different blood collection, sample matrix, and immunoassay methods in a prenatal screening setting

We compared how measurements of pregnancy-associated plasma protein A (PAPP-A) and the free beta subunit of human chorionic gonadotropin (fβ-hCG) in maternal blood are influenced by different methods for blood collection, sample matrix, and immunoassay platform. Serum and dried blood spots (DBS) were obtained by venipuncture and by finger prick of 19 pregnant women. PAPP-A and fβ-hCG from serum and from DBS were measured by conventional indirect immunoassay on an AutoDELFIA platform and by antibody microarray. We compared methods based on the recoveries for both markers as well as marker levels correlations across samples. All method comparisons showed high correlations for both marker concentrations. Recovery levels of PAPP-A from DBS were 30% lower, while those of fβ-hCG from DBS were 50% higher compared to conventional venipuncture serum. The recoveries were not affected by blood collection or immunoassay method. The high correlation coefficients for both markers indicate that DBS from finger prick can be used reliably in a prenatal screening setting, as a less costly and minimally invasive alternative for venipuncture serum, with great logistical advantages. Additionally, the use of antibody arrays will allow for extending the number of first trimester screening markers on maternal and fetal health.

Pharmacokinetic-pharmacodynamic study of subcutaneous injection of depot nandrolone decanoate using dried blood spots sampling coupled with ultrapressure liquid chromatography tandem mass spectrometry assays

CONTEXT

Testosterone (T) and nandrolone (N) esters require deep im injections by medical personnel but these often deposit injectate into sc fat so that more convenient sc self-administration may be feasible.

OBJECTIVE

To investigate the feasibility and pharmacology of sc injection of N decanoate in healthy men using dried blood spot (DBS) for frequent blood sampling without clinic visits.

SETTING AND DESIGN

Healthy male volunteers received 100 mg N decanoate by a single sc injection. Finger-prick capillary blood was spotted onto filter paper before injection daily at home for 21 d and stored at room temperature. Venous whole blood was also spotted onto filter paper before and weekly for 3 wk after injection. DBS were extracted for assay of N and T by liquid chromatography tandem mass spectrometry in a single batch with serum concentrations estimated with adjustment for capillary blood sample volume and hematocrit to define peak (N) or nadir (T) time and concentration from individual daily measurements.

RESULTS

Daily serum N peaked 2.50 ± 0.25 (SEM) ng/mL at a median (range) of 6 (4-13) days causing a reduction in serum T from 3.50 ± 0.57 ng/mL at baseline to a nadir of 0.38 ± 0.13 (SEM) ng/mL (89 ± 3% suppression) at a median (range) of 8 (5-16) days. Simultaneously sampled capillary, venous whole blood, and serum gave almost identical results for serum T and N. Finger-pricks and sc injections were well tolerated.

CONCLUSIONS

This study demonstrates that A) DBS sampling with liquid chromatography mass spectrometry steroid analysis achieves frequent time sampling in the community without requiring clinic visits, venesection, or frozen serum storage, and B) androgen esters in an oil vehicle can be delivered effectively by sc injection, thus avoiding the need for medically supervised deep-im injections.

Quantification of sulfatides in dried blood and urine spots from metachromatic leukodystrophy patients by liquid chromatography/electrospray tandem mass spectrometry

BACKGROUND

Treatments are being developed for metachromatic leukodystrophy (MLD), suggesting the need for eventual newborn screening. Previous studies have shown that sulfatide molecular species are increased in the urine of MLD patients compared to samples from non-MLD individuals, but there is no data using dried blood spots (DBS), the most common sample available for newborn screening laboratories.

METHODS

We used ultra-high performance liquid chromatography/tandem mass spectrometry (UHPLC/MS/MS) to quantify sulfatides in DBS and dried urine spots from 14 MLD patients and 50 non-MLD individuals.

RESULTS

Several sulfatide molecular species were increased in dried urine samples from all MLD samples compared to non-MLD samples. Sulfatides, especially low molecular species, were increased in DBS from MLD patients, but the sulfatide levels were relatively low. There was good separation in sulfatide levels between MLD and non-MLD samples when dried urine spots were used, but not with DBS, because DBS from non-MLD individuals have measurable levels of sulfatides.

CONCLUSION

Sulfatide accumulation studies in urine, but not in DBS, emerges as the method of choice if newborn screening is to be proposed for MLD.

First experience with a fully automated extraction system for simultaneous on-line direct tandem mass spectrometric analysis of amino acids and (acyl-)carnitines in a newborn screening setting

RATIONALE

For Newborn Screening (NBS) programs all over the world whole blood dried on filter paper, also referred to as dried blood spots (DBS), has been the standard specimen for decades. In recent years DBS have attracted the attention of pharmaceutical companies, mostly due to the low volume of collected sample and simplified, therefore more cost-efficient, transportation requirements. However, the classical NBS workflow did not totally fulfil the needs of their studies, especially with respect to high-throughput unassisted sample processing for tandem mass spectrometric (MS/MS) analysis. Automated on-line extraction systems for direct analysis have already been tested and proved to be suitable for these pharmaceutical applications.

METHODS

The suitability of the automated CAMAG DBS-MS 500 interface for simultaneous detection of amino acids and (acyl-)carnitines has been tested together with an Acquity TQD tandem mass spectrometer from Waters and MassChrom stable isotope labelled internal standards from Chromsystems. No chromatographic sample treatment was applied; instead, the extract was directly injected into the MS/MS instrument. The feasibility of the instrumental setting for the routine newborn screening was tested on original samples coming from previously diagnosed patients.

RESULTS

The performance of the automated extraction technique and its application in preliminary quantitative screening for amino acids and (acyl-)carnitines for NBS showed very promising results. Several samples from patients, each diagnosed with one of four different inborn errors of metabolism (IEM), were tested and the correlation with the conventional punch-and-elute approach was very good.

CONCLUSIONS

Although the presented method still needs further optimization, our study clearly shows the possibility to use direct on-line analysis in the NBS setting. Our report on direct on-line analysis of newborn samples is a first approach in the development of a fully automated screening method for NBS analysis. With regard to the chemical properties of the analytes, the study resulted in a readily applicable screening method.

Current and future use of "dried blood spot" analyses in clinical chemistry

The analysis of blood spotted and dried on a matrix (i.e., "dried blood spot" or DBS) has been used since the 1960s in clinical chemistry; mostly for neonatal screening. Since then, many clinical analytes, including nucleic acids, small molecules and lipids, have been successfully measured using DBS. Although this pre-analytical approach represents an interesting alternative to classical venous blood sampling, its routine use is limited. Here, we review the application of DBS technology in clinical chemistry, and evaluate its future role supported by new analytical methods such as mass spectrometry.

Ultra-performance liquid chromatography/tandem mass spectrometry for determination of sulfatides in dried blood spots from patients with metachromatic leukodystrophy

RATIONALE

Metachromatic leukodystrophy (MLD) is a genetic autosomal recessive disease caused by a deficiency in arylsulfatase A. Accumulated sulfatides can be detected in the urine and detection of sulfatiduria is a useful test for diagnosis and monitoring. To our knowledge, no studies have explored the accumulation of sulfatides in dried blood spots (DBSs). We developed an ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method for measuring sulfatides in DBSs from patients with MLD.

METHODS

DBSs were eluted with internal standard. After mixing and centrifugation, the organic layer was transferred to a 96-well microplate and dried, then resuspended in methanol/propanol solution. Samples were analyzed on an UPLC system. Total running time was 4 min. Quantification was achieved by multiple reaction monitoring using a tandem mass spectrometer. We evaluated the precision, linearity, and ion suppression of the method and analyzed sulfatide concentrations in DBS specimens from MLD patients (n = 9), pseudodeficiency (PD) patient (n = 1), obligate heterozygotes (OH) (n = 2) and normal controls (n = 124).

RESULTS

In negative-ion mode, sulfatides species subjected to collision-induced dissociation readily fragment to produce an intense ion at m/z 96.8 (HSO4(-)). The precisions of low and high concentration controls ranged from 5.4 to 19.9%. The sulfatides produced linear responses. Molecular species of sulfatides were barely detected in DBSs from normal individuals and the PD-OH group [mean (range), 0.07 (<0.05-0.34) and 0.13 (<0.05-0.22) µg/mL, respectively]. In contrast, the DBSs from MLD patients showed a marked increase in several molecular species of sulfatide [mean (range), 2.02 (1.18-3.89) µg/mL].

CONCLUSIONS

Simultaneous detection for sulfatides using UPLC/MS/MS can be successfully applied to DBS analysis. This method provides a fast and effective screening and monitoring tool for the diagnosis and treatment of MLD.

Systematic review of the use of dried blood spots for monitoring HIV viral load and for early infant diagnosis

BACKGROUND

Dried blood spots (DBS) have been used as alternative specimens to plasma to increase access to HIV viral load (VL) monitoring and early infant diagnosis (EID) in remote settings. We systematically reviewed evidence on the performance of DBS compared to plasma for VL monitoring and EID.

METHODS AND FINDINGS

Thirteen peer reviewed HIV VL publications and five HIV EID papers were included. Depending on the technology and the viral load distribution in the study population, the percentage of DBS samples that are within 0.5 log of VL in plasma ranged from 52-100%. Because the input sample volume is much smaller in a blood spot, there is a risk of false negatives with DBS. Sensitivity of DBS VL was found to be 78-100% compared to plasma at VL below 1000 copies/ml, but this increased to 100% at a threshold of 5000 copies/ml. Unlike a plasma VL test which measures only cell free HIV RNA, a DBS VL also measures proviral DNA as well as cell-associated RNA, potentially leading to false positive results when using DBS. The systematic review showed that specificity was close to 100% at DBS VL above 5000 copies/ml, and this threshold would be the most reliable for predicting true virologic failure using DBS. For early infant diagnosis, DBS has a sensitivity of 100% compared to fresh whole blood or plasma in all studies.

CONCLUSIONS

Although limited data are available for EID, DBS offer a highly sensitive and specific sampling strategy to make viral load monitoring and early infant diagnosis more accessible in remote settings. A standardized approach for sampling, storing, and processing DBS samples would be essential to allow successful implementation.

TRIAL REGISTRATION

PROSPERO Registration #: CRD42013003621.

Carnitine levels in 26,462 individuals from the nationwide screening program for primary carnitine deficiency in the Faroe Islands

BACKGROUND

Primary carnitine deficiency (PCD) is an autosomal recessive disorder of fatty acid oxidation and has been associated to episodes of sudden death in the Faroe Islands. Data are presented from the nationwide population based Faroese screening program to find people with low carnitine levels indicating PCD.

METHODS

Whole blood samples from dried blood spots were analysed by tandem mass spectrometry with and without butylation. Genetic analyses were performed in all people with non-butylated free carnitine (fC0) below 7 μmol/L.

RESULTS

55 % (n = 26,462) of the entire population was screened and 89 PCD patients were identified, yielding an overall prevalence of 1:297 of PCD in the Faroe Islands. Carnitine levels were positively correlated to age in both males and females (p < 0.003) although levels decreased in females when reaching fertile age. The gender difference in mean carnitine levels was significant during female fertile age (4.71 μmol/L fC0 in the age group 25-30 years, p < 0.01). A lower cut-off of 5 μmol/L in fC0 identified all homozygous for the severe genotype c.95A > G (p.N32S) (n = 20).

CONCLUSION

Carnitine levels differ by gender and age. A lower cut-off of 5 μmol/L in fC0 was appropriate to identify c.95A > G homozygotes. The prevalence of PCD in the Faroe Islands is the highest reported in the world (1:297).

Performance of serum and dried blood spot acylcarnitine profiles for detection of fatty acid β-oxidation disorders in adult patients with rhabdomyolysis

BACKGROUND

Plasma/serum and dried blood spot (DBS) acylcarnitine profiles (ACPs) are key to the diagnosis of mitochondrial fatty acid β-oxidation disorders (FAODs). Despite their significant clinical applications, limited published data exists to compare their sensitivities and specificities. We retrospectively evaluated these two methods in adult patients with a history of rhabdomyolysis; investigated for an underlying FAOD.

METHODS

A retrospective study was completed for adult patients (investigated between 2003 and 2011) meeting the inclusion criteria of a history of recurrent rhabdomyolysis or one episode of rhabdomyolysis with a history of exercise intolerance. All subjects underwent investigations for an underlying FAOD including DBS and serum ACP analysis concurrently collected during a symptom-free period, and skin biopsy for cultured fibroblast fatty acid oxidation studies or enzyme activity measurement, as indicated, with or without molecular confirmation. Their medical records were reviewed, and the performance of the two methods were compared.

RESULTS

Seven out of 31 subjects (22.6 %) were diagnosed with an underlying FAOD. Long chain acylcarnitines were more markedly elevated in serum samples from confirmed CPTII cases (n = 4) as compared to matched DBS profiles. The sensitivity and specificity of DBS ACP was 71.4 % (95 % CI, 0.30-0.95) and 100 % (95 % CI, 0.79-1.00), respectively, compared to a sensitivity of 100 % (95 % CI, 0.56-1.00) and a specificity of 94.7 % (95 % CI, 0.72-1.00) for serum ACP.

CONCLUSION

FAODs appear to be a common cause of recurrent rhabdomyolysis or rhabdomyolysis with a history of exercise induced myalgia. At least historically, FAODs maybe underdiagnosed in adults with rhabdomyolysis. This study suggests that serum ACP might be more sensitive than DBS ACP for detection of an underlying FAOD in adults with rhabdomyolysis while asymptomatic.

Feasibility of newborn screening for guanidinoacetate methyltransferase (GAMT) deficiency

Guanidinoacetate methyltransferase (GAMT) deficiency causes brain creatine deficiency characterized by developmental delays, speech delay, seizures and autism-like behavior. Identification and therapy at birth because of a positive family history has prevented intellectual disability and seizures in all cases reported. The objective of this study was to develop a method to identify patients with GAMT deficiency from newborn screening blood spots. Creatine and guanidinoacetate were extracted from 10,000 deidentified blood spots using the same protocol routinely used for newborn screening and quantified by stable isotope dilution using deuterated creatine and guanidinoacetate as internal standards. Residual dried blood spots from three infants with GAMT deficiency were used to evaluate the sensitivity of the method. A second tier test using UPLC-MS/MS was performed to analyze samples with a concentration of guanidinoacetate >2.44 μmol/L (99.5th centile of the normal population). Fifty four blood spots required second tier testing in addition to seven blood spots from three patients with GAMT deficiency retrospectively analyzed. With second tier testing, only the samples from GAMT deficiency patients had elevated concentration of guanidinoacetate. Our results show that GAMT deficiency can be identified in newborns using routine extraction methods. The cost of this additional screening is minimal, as it does not require additional instrumentation, procedure, or sample collection. The use of a second tier test can reduce the false positive rate to a minimum. Summary Brain creatine deficiency syndromes cause mental retardation that can be prevented if therapy is initiated early in life. This manuscript reports that infants with GAMT deficiency (one of the brain creatine deficiency syndromes) can be identified from elevated guanidinoacetate in newborn blood spots with virtually absent false-positive results using a second tier test.

A novel dried blood spot-LCMS method for the quantification of methotrexate polyglutamates as a potential marker for methotrexate use in children

Objective

Development and validation of a selective and sensitive LCMS method for the determination of methotrexate polyglutamates in dried blood spots (DBS).

Methods

DBS samples [spiked or patient samples] were prepared by applying blood to Guthrie cards which was then dried at room temperature. The method utilised 6-mm disks punched from the DBS samples (equivalent to approximately 12 µl of whole blood). The simple treatment procedure was based on protein precipitation using perchloric acid followed by solid phase extraction using MAX cartridges. The extracted sample was chromatographed using a reversed phase system involving an Atlantis T3-C18 column (3 µm, 2.1×150 mm) preceded by Atlantis guard column of matching chemistry. Analytes were subjected to LCMS analysis using positive electrospray ionization.

Key Results

The method was linear over the range 5–400 nmol/L. The limits of detection and quantification were 1.6 and 5 nmol/L for individual polyglutamates and 1.5 and 4.5 nmol/L for total polyglutamates, respectively. The method has been applied successfully to the determination of DBS finger-prick samples from 47 paediatric patients and results confirmed with concentrations measured in matched RBC samples using conventional HPLC-UV technique.

Conclusions and Clinical Relevance

The methodology has a potential for application in a range of clinical studies (e.g. pharmacokinetic evaluations or medication adherence assessment) since it is minimally invasive and easy to perform, potentially allowing parents to take blood samples at home. The feasibility of using DBS sampling can be of major value for future clinical trials or clinical care in paediatric rheumatology.

An overview of the clinical use of filter paper in the diagnosis of tropical diseases

Tropical infectious diseases diagnosis and surveillance are often hampered by difficulties of sample collection and transportation. Filter paper potentially provides a useful medium to help overcome such problems. We reviewed the literature on the use of filter paper, focusing on the evaluation of nucleic acid and serological assays for diagnosis of infectious diseases using dried blood spots (DBS) compared with recognized gold standards. We reviewed 296 eligible studies and included 101 studies evaluating DBS and 192 studies on other aspects of filter paper use. We also discuss the use of filter paper with other body fluids and for tropical veterinary medicine. In general, DBS perform with sensitivities and specificities similar or only slightly inferior to gold standard sample types. However, important problems were revealed with the uncritical use of DBS, inappropriate statistical analysis, and lack of standardized methodology. DBS have great potential to empower healthcare workers by making laboratory-based diagnostic tests more readily accessible, but additional and more rigorous research is needed.

A practical fluorometric assay method to measure lysosomal acid lipase activity in dried blood spots for the screening of cholesteryl ester storage disease and Wolman disease

Fluorometric measurements of 4-methylumbelliferone (4-MU) are generally used to screen lysosomal storage diseases (LSDs) using dried blood spots (DBSs). However, in DBS, it is difficult to measure lysosomal acid lipase (LAL) activity due to the influence of other lipases in whole blood. Recently, Hamilton used a fluorometric enzyme assay with 4-MU derivatives to measure the LAL activity in DBS. This method requires mercury chloride as stopping reagent, and the fluorescence intensity of 4-MU was measured at an acidic pH. We report a revised method to measure the LAL activity without using toxic mercury chloride and to measure the fluorescence intensity of 4-MU at a basic pH. For this measurement, we established a more practical method that does not require mercury chloride. The LAL activity in DBS was measured in 51 normal controls, seven obligate carriers and seven patients with CESD. The average LAL activities ± SD in the DBS from the normal, obligate carriers and CESD patients were 0.68 ± 0.2 (range: 0.3-1.08), 0.21 ± 0.1 (range: 0.11-0.41) and 0.02 ± 0.02 (range: 0-0.06) nmol/punch/h, respectively. There was a significant difference between the normal and the CESD. Our method does not require toxic mercury chloride and is an appropriate revised enzyme assay using DBS for screening patients with CESD.

Analysis of dried blood spots using DESI mass spectrometry

Dried blood spot (DBS) analysis using mass spectrometry is an invaluable technique for examining blood markers of inborn metabolic diseases in clinical laboratories. Implementation of DBS sampling and analysis in pharmaceutical development have more recently gained traction due to the advantages of convenience in sample procurement and logistics, as well as the innate advantages associated with the collection of lower blood volumes. While there are several realized advantages of DBS, the bioanalytical laboratory is disadvantaged and burdened with additional preparative steps prior to analysis. Therefore, improvements in the laboratory workflow for DBS analysis are necessary. Here, we describe direct blood spot analysis using desorption electrospray ionization (DESI) mass spectrometry for quantitative determination of drugs in whole blood.

A microfluidic device for dry sample preservation in remote settings

This paper describes a microfluidic device for dry preservation of biological specimens at room temperature that incorporates chemical stabilization matrices. Long-term stabilization of samples is crucial for remote medical analysis, biosurveillance, and archiving, but the current paradigm for transporting remotely obtained samples relies on the costly "cold chain" to preserve analytes within biospecimens. We propose an alternative approach that involves the use of microfluidics to preserve samples in the dry state with stabilization matrices, developed by others, that are based on self-preservation chemistries found in nature. We describe a SlipChip-based device that allows minimally trained users to preserve samples with the three simple steps of placing a sample at an inlet, closing a lid, and slipping one layer of the device. The device fills automatically, and a pre-loaded desiccant dries the samples. Later, specimens can be rehydrated and recovered for analysis in a laboratory. This device is portable, compact, and self-contained, so it can be transported and operated by untrained users even in limited-resource settings. Features such as dead-end and sequential filling, combined with a "pumping lid" mechanism, enable precise quantification of the original sample's volume while avoiding overfilling. In addition, we demonstrated that the device can be integrated with a plasma filtration module, and we validated device operations and capabilities by testing the stability of purified RNA solutions. These features and the modularity of this platform (which facilitates integration and simplifies operation) would be applicable to other microfluidic devices beyond this application. We envision that as the field of stabilization matrices develops, microfluidic devices will be useful for cost-effectively facilitating remote analysis and biosurveillance while also opening new opportunities for diagnostics, drug development, and other medical fields.

A novel Cookson-type reagent for enhancing sensitivity and specificity in assessment of infant vitamin D status using liquid chromatography/tandem mass spectrometry

RATIONALE

25-Hydroxyvitamin D3 [25(OH)D3] is the best-established indicator of vitamin D status. 4-Phenyl-1,2,4-triazoline-3,5-dione (PTAD), a representative Cookson-type reagent, has often been employed for enhancing the sensitivity in the trace determination of 25(OH)D3 in a neonatal dried blood spot (DBS), which contains only 2.65 μL of whole blood, using liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS). The objective of this study was the development of a novel Cookson-type reagent surpassing PTAD in terms of sensitivity and specificity in the LC/ESI-MS/MS assay of 25(OH)D3.

METHODS

A novel Cookson-type reagent, 4-(4'-dimethylaminophenyl)-1,2,4-triazoline-3,5-dione (DAPTAD), was synthesized from 4-dimethylaminobenzoyl chloride. The DAPTAD-derivative of 25(OH)D3 was prepared and its LC/ESI-MS/MS behavior was examined. The applicability of the DAPTAD-derivatization in the determination of 25(OH)D3 in neonatal DBSs was also examined.

RESULTS

The derivatization was completed at room temperature within 1 h. The DAPTAD-derivative of 25(OH)D3 provided a characteristic product ion derived from the cleavage of the vitamin D skeleton during MS/MS. The limit of detection of the DAPTAD-derivative during selected reaction monitoring was 0.25 fmol on the column, which was 30 and 2 times lower than those of the intact 25(OH)D3 and the PTAD-derivative, respectively. The DAPTAD-derivatization followed by LC/ESI-MS/MS enabled the detection of a trace amount (in the low-ng/mL range) of 25(OH)D3 in DBSs with a simple pretreatment (only methanol extraction) and short chromatographic run time (10 min). The DAPTAD-derivatization was also useful for the separation of 25(OH)D3 from a potent interfering metabolite, 3-epi-25-hydroxyvitamin D3 [3-epi-25(OH)D3]. On the contrary, the assay using the PTAD-derivatization might lead to overestimation of the true 25(OH)D3 levels due to the co-elution of 25(OH)D3 and 3-epi-25(OH)D3.

CONCLUSIONS

We developed DAPTAD for enhancing the sensitivity and specificity of the LC/ESI-MS/MS assay of 25(OH)D3. Our new method using DAPTAD can reduce the overestimation of the 25(OH)D3 levels, and will prove helpful in the diagnosis of vitamin D deficiency in infants.

Simple paper-based test for measuring blood hemoglobin concentration in resource-limited settings

BACKGROUND

The measurement of hemoglobin concentration ([Hb]) is performed routinely as a part of a complete blood cell count to evaluate the oxygen-carrying capacity of blood. Devices currently available to physicians and clinical laboratories for measuring [Hb] are accurate, operate on small samples, and provide results rapidly, but may be prohibitively expensive for resource-limited settings. The unavailability of accurate but inexpensive diagnostic tools often precludes proper diagnosis of anemia in low-income developing countries. Therefore, we developed a simple paper-based assay for measuring [Hb].

METHODS

A 20-μL droplet of a mixture of blood and Drabkin reagent was deposited onto patterned chromatography paper. The resulting blood stain was digitized with a portable scanner and analyzed. The mean color intensity of the blood stain was used to quantify [Hb]. We compared the performance of the paper-based Hb assay with a hematology analyzer (comparison method) using blood samples from 54 subjects.

RESULTS

The values of [Hb] measured by the paper-based assay and the comparison method were highly correlated (R(2) = 0.9598); the standard deviation of the difference between the two measurements was 0.62 g/dL. The assay was accurate within 1 g/dL 90.7% of the time, overestimating [Hb] by ≥1 g/dL in 1.9% and underestimating [Hb] by ≥1 g/dL in 7.4% of the subjects.

CONCLUSIONS

This study demonstrates the feasibility of the paper-based Hb assay. This simple, low-cost test should be useful for diagnosing anemia in resource-limited settings, particularly in the context of care for malaria, HIV, and sickle cell disease patients in sub-Saharan Africa.

Comparison of proteins in whole blood and dried blood spot samples by LC/MS/MS

Dried blood spot (DBS) sampling methods are desirable for population-wide biomarker screening programs because of their ease of collection, transportation, and storage. Immunoassays are traditionally used to quantify endogenous proteins in these samples but require a separate assay for each protein. Recently, targeted mass spectrometry (MS) has been proposed for generating highly-multiplexed assays for biomarker proteins in DBS samples. In this work, we report the first comparison of proteins in whole blood and DBS samples using an untargeted MS approach. The average number of proteins identified in undepleted whole blood and DBS samples by liquid chromatography (LC)/MS/MS was 223 and 253, respectively. Protein identification repeatability was between 77%-92% within replicates and the majority of these repeated proteins (70%) were observed in both sample formats. Proteins exclusively identified in the liquid or dried fluid spot format were unbiased based on their molecular weight, isoelectric point, aliphatic index, and grand average hydrophobicity. In addition, we extended this comparison to include proteins in matching plasma and serum samples with their dried fluid spot equivalents, dried plasma spot (DPS), and dried serum spot (DSS). This work begins to define the accessibility of endogenous proteins in dried fluid spot samples for analysis by MS and is useful in evaluating the scope of this new approach.

Archived neonatal dried blood spot samples can be used for accurate whole genome and exome-targeted next-generation sequencing

Dried blood spot samples (DBSS) have been collected and stored for decades as part of newborn screening programmes worldwide. Representing almost an entire population under a certain age and collected with virtually no bias, the Newborn Screening Biobanks are of immense value in medical studies, for example, to examine the genetics of various disorders. We have previously demonstrated that DNA extracted from a fraction (2×3.2mm discs) of an archived DBSS can be whole genome amplified (wgaDNA) and used for accurate array genotyping. However, until now, it has been uncertain whether wgaDNA from DBSS can be used for accurate whole genome sequencing (WGS) and exome sequencing (WES). This study examined two individuals represented by three different types of samples each: whole-blood (reference samples), 3-year-old DBSS spotted with reference material (refDBSS), and 27- to 29-year-old archived neonatal DBSS (neoDBSS) stored at -20°C in the Danish Newborn Screening Biobank. The reference samples were genotyped using an Illumina Omni2.5M array, and all samples were sequenced on a HighSeq2000 Paired-End flow cell. First, we compared the array single nucleotide polymorphism (SNP) genotype data to the single nucleotide variation (SNV) calls from the WGS and WES SNV calls. We also compared the WGS and WES reference sample SNV calls to the DBSS SNV calls. The overall performance of the archived DBSS was similar to the whole blood reference sample. Plotting the error rates relative to coverage revealed that the error rates of DBSS were similar to that of their reference samples. SNVs called with a coverage<×8 had error rates between 1.5 and 35%, whereas the error rates of SNVs called with a coverage≥8 were <1.5%. In conclusion, the wgaDNA amplified from both new and old neonatal DBSS perform as well as their whole-blood reference samples with regards to error rates, strongly indicating that neonatal DBSS collected shortly after birth and stored for decades comprise an excellent resource for NGS studies of disease.

Filter paper blood spot enzyme linked immunoassay for adiponectin and application in the evaluation of determinants of child insulin sensitivity

BACKGROUND

Adiponectin is an adipocyte-derived hormone that acts as a marker of insulin sensitivity. Bloodspot sampling by fingerstick onto filter paper may increase the feasibility of large-scale studies of the determinants of insulin sensitivity. We first describe the validation of an enzyme-linked immunoassay (ELISA) for quantifying adiponectin from dried blood spots and then demonstrate its application in a large trial (PROBIT).

METHODS

We quantified adiponectin from 3-mm diameter discs (≈3 µL of blood) punched from dried blood spots obtained from: i) whole blood standards (validation); and ii) PROBIT trial samples (application) in which paediatricians collected blood spots from 13,879 children aged 11.5 years from 31 sites across Belarus. We examined the distribution of bloodspot adiponectin by demographic and anthropometric factors, fasting insulin and glucose.

RESULTS

In the validation study, mean intra-assay coefficients of variation (n=162) were 15%, 13% and 10% for 'low' (6.78 µg/ml), 'medium' (18.18 µg/ml) and 'high' (33.13 µg/ml) internal quality control (IQC) samples, respectively; the respective inter-assay values (n=40) were 23%, 21% and 14%. The correlation coefficient between 50 paired whole bloodspot versus plasma samples, collected simultaneously, was 0.87 (95% CI: 0.78 to 0.93). Recovery of known quantities of adiponectin (between 4.5 to 36 µg/ml) was 100.3-133%. Bloodspot adiponectin was stable for at least 30 months at -80°C. In PROBIT, we successfully quantified fasting adiponectin from dried blood spots in 13,329 of 13,879 (96%) children. Mean adiponectin (standard deviation) concentrations were 17.34 µg/ml (7.54) in boys and 18.41 µg/ml (7.92) in girls and were inversely associated with body mass index, fat mass, triceps and subscapular skin-fold thickness, waist circumference, height and fasting glucose.

CONCLUSIONS

Bloodspot ELISA is suitable for measuring adiponectin in very small volumes of blood collected on filter paper and can be applied to large-scale studies.

Stabilities of hemoglobins A and S in dried blood spots stored under controlled conditions

OBJECTIVE

We aimed to measure separately the contributions of heat and humidity to changes in levels of hemoglobins A and S in dried-blood-spot (DBS) samples.

DESIGN AND METHODS

We stored paired sets of DBSs at 37°C for predetermined intervals in low-humidity and high-humidity environments. Hemoglobin A and S levels of all samples in each complete set were measured in a single high performance liquid chromatography run.

RESULTS

During the one-month storage intervals, both hemoglobin species lost about 35% of initial levels in low-humidity storage and almost all of initial levels in high-humidity storage.

CONCLUSIONS

Minimizing both humidity and temperature in the transportation and storage environments of DBS samples is essential to maintaining the integrity of the hemoglobin tetramer molecules.

Matrix-assisted laser desorption/ionization for simultaneous quantitation of (acyl-)carnitines and organic acids in dried blood spots

RATIONALE

Screening for inborn errors of metabolism using mass spectrometry is part of nationwide newborn screening programs and involves the detection of disease relevant (acyl-)carnitines and organic acids from dried blood spots. Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry (MALDI-MS) is a well-established tool for proteomics approaches. In recent years, this technique has become more and more integrated in analysis and identification of small metabolites and disease biomarkers in daily clinical laboratories.

METHODS

We used a combination of both MALDI and high-resolution accurate mass (HR/AM) mass spectrometry using a linear ion trap-Orbitrap for the identification of small molecules from dried blood spots that serve as biomarkers for inborn errors of metabolism. The levels of detected metabolite species were compared between healthy newborns and affected patients with various inborn errors of metabolism using isotopically labeled internal standards and new bioinformatics software, respectively.

RESULTS

(Acyl-)carnitine levels from normal and affected patients could be quantified and differentiated. Additionally, using the high resolving power of full scan Orbitrap mass spectrometry and novel software tools we demonstrated the identification and quantification of disease-specific organic acids.

CONCLUSIONS

MALDI-HR/AM and full scan spectra to obtain information for the metabolic status of patients is a promising complementary approach to electrospray ionization mass spectrometry by simplified sample preparation, facilitating the screening of hundreds of metabolites from small sample volumes.

Rapid assays for Gaucher and Hurler diseases in dried blood spots using digital microfluidics

OBJECTIVE

Easy tool for newborn screening of Gaucher and Hurler diseases.

METHODS

Method comparison between fluorometric enzymatic activity assay on a digital microfluidic platform and micro-titer plate bench assay was performed on normal (n = 100), Gaucher (n = 10) and Hurler (n = 7) dried blood spot samples.

RESULTS

Enzymatic activity analysis of glucocerebrosidase (Gaucher) and α-l-iduronidase (Hurler) revealed similar discrimination between normal and affected samples on both platforms.

CONCLUSIONS

Digital microfluidics is suitable for Gaucher and Hurler newborn screening.

DNA methylome profiling using neonatal dried blood spot samples: a proof-of-principle study

DNA methylation is the most common DNA modification and perhaps the best described epigenetic modification. It is believed to be important for genomic imprinting and gene regulation and has been associated with the development of diseases such as schizophrenia and some types of cancer. Neonatal dried blood spot samples, commonly known as Guthrie cards, are routinely collected worldwide to screen newborns for diseases. Some countries, including Denmark, have been storing the excess neonatal dried blood spot samples in biobanks for decades. Representing a high percentage of the population under a certain age, the neonatal dried blood spot samples are a potential alternative to collecting new samples to study diseases. As such, neonatal dried blood spot samples have previously been used for DNA genotyping studies with excellent results. However, the amount of material available for research is often limited, challenging researchers to generate the most data from a limited quantity of material. In this proof-of-principle study, we address whether two 3.2mm disks punched from a neonatal dried blood spot sample contain enough DNA for genome-wide methylome profiling, measuring 27,578 loci at the same time. We selected two subjects and carried out the following with each: 1) collected an adult whole-blood sample as reference, 2) spotted a fraction of the whole-blood sample onto a similar type of filter paper as used in the newborn screening and stored it for 3years to serve as a dried blood spot reference, and 3) identified the archived neonatal dried blood spot samples, stored for 26-28years, in the Danish Newborn Screening Biobank as a representative of the archived samples. For comparison, we used two different kits for DNA extraction. The DNA, extracted using the Extract-N-Amp Blood PCR kit, was analyzed, and no statistically significant differences were observed (P<0.001) when we compared the methylation profile of the reference whole-blood samples to the dried blood spot references. This indicates that two 3.2mm disks contain enough material for reliable methylome profiling and that storing the whole-blood sample on neonatal dried blood spot filter paper for 3years does not interfere with the outcome of the analysis. Furthermore, we compared the adult DNA methylation profile to the neonatal dried blood spot sample profile. Approximately 50 sites in the subjects were significantly (P<0.001) different in the newborn sample compared with the adult sample. Both being healthy adults and the high quality of the DNA methylation array led to the conclusion that the archived neonatal dried blood spot samples can be used for methylome profiling, despite decades of storage and DNA degradation. In conclusion, we show that reliable methylome data can be obtained from old neonatal dried blood spot samples, by using a reasonable amount of the limited resource. This further adds to the use of neonatal dried blood spot samples in genetic research and screening and paves the way for unique population-based studies of epigenetic modifications after birth.

Visual automated fluorescence electrophoresis provides simultaneous quality, quantity, and molecular weight spectra for genomic DNA from archived neonatal blood spots

The Guthrie 903 card archived dried blood spots (DBSs) are a unique but terminal resource amenable for individual and population-wide genomic profiling. The limited amounts of DBS-derived genomic DNA (gDNA) can be whole genome amplified, producing sufficient gDNA for genomic applications, albeit with variable success; optimizing the isolation of high-quality DNA from these finite, low-yield specimens is essential. Agarose gel electrophoresis and spectrophotometry are established postextraction quality control (QC) methods but lack the power to disclose detailed structural, qualitative, or quantitative aspects that underlie gDNA failure in downstream applications. Visual automated fluorescence electrophoresis (VAFE) is a novel QC technology that affords precise quality, quantity, and molecular weight of double-stranded DNA from a single microliter of sample. We extracted DNA from 3-mm DBSs archived in the Swedish Neonatal Repository for >30 years and performed the first quantitative and qualitative analyses of DBS-derived DNA on VAFE, before and after whole genome amplified, in parallel with traditional QC methods. The VAFE QC data were correlated with subsequent sample performance in PCR, sequencing, and high-density comparative genome hybridization array. We observed improved standardization of nucleic acid quantity, quality and integrity, and high performance in the downstream genomic technologies. Addition of VAFE measures in QC increases confidence in the validity of genetic data and allows cost-effective downstream analysis of gDNA for investigational and diagnostic applications.

Multiplexed quantitation of endogenous proteins in dried blood spots by multiple reaction monitoring-mass spectrometry

Dried blood spot (DBS) sampling, coupled with multiple reaction monitoring mass spectrometry (MRM-MS), is a well-established approach for quantifying a wide range of small molecule biomarkers and drugs. This sampling procedure is simpler and less-invasive than those required for traditional plasma or serum samples enabling collection by minimally trained personnel. Many analytes are stable in the DBS format without refrigeration, which reduces the cost and logistical challenges of sample collection in remote locations. These advantages make DBS sample collection desirable for advancing personalized medicine through population-wide biomarker screening. Here we expand this technology by demonstrating the first multiplexed method for the quantitation of endogenous proteins in DBS samples. A panel of 60 abundant proteins in human blood was targeted by monitoring proteotypic tryptic peptides and their stable isotope-labeled analogs by MRM. Linear calibration curves were obtained for 40 of the 65 peptide targets demonstrating multiple proteins can be quantitatively extracted from DBS collection cards. The method was also highly reproducible with a coefficient of variation of <15% for all 40 peptides. Overall, this assay quantified 37 proteins spanning a range of more than four orders of magnitude in concentration within a single 25 min LC/MRM-MS analysis. The protein abundances of the 33 proteins quantified in matching DBS and whole blood samples showed an excellent correlation, with a slope of 0.96 and an R(2) value of 0.97. Furthermore, the measured concentrations for 80% of the proteins were stable for at least 10 days when stored at -20 °C, 4 °C and 37 °C. This work represents an important first step in evaluating the integration of DBS sampling with highly-multiplexed MRM for quantitation of endogenous proteins.

Blood and dried blood spot telomere length measurement by qPCR: assay considerations

Measurement of telomere length is crucial for the study of telomere maintenance and its role in molecular pathophysiology of diseases and in aging. Several methods are used to measure telomere length, the choice of which usually depends on the type and size of sample to be assayed, as well as cost and throughput considerations. The goal of this study was to investigate the factors that may influence the reliability of qPCR-based relative telomere length measurements in whole blood. Day to day intra-individual variability, types of blood anticoagulant, sample storage conditions, processing and site of blood draw were investigated. Two qPCR-based methods to measure telomere length (monoplex vs. multiplex) were also investigated and showed a strong correlation between them. Freezing and thawing of the blood and storage of the blood at 4°C for up to 4 days did not affect telomere length values. Telomere lengths in dried blood spots were significantly higher than both whole blood and peripheral mononuclear blood cells, and were highly correlated with both. We found that telomere length measurements were significantly higher in dried blood spots collected directly from fingertip prick compared to dried blood spots prepared with anticoagulated whole blood collected from the finger, and non-blotted whole blood taken from both finger and arm venipuncture. This suggests that DNA from cells blotted on paper is not equivalent to that collected from venipuncture whole blood, and caution should be taken when comparing between blood sample types.

A hepatitis C avidity test for determining recent and past infections in both plasma and dried blood spots

BACKGROUND

DBS testing has been used successfully to detect HCV antibody positive individuals. Determining how long someone has been infected is important for surveillance initiatives. Antibody avidity is a method that can be used to calculate recency of infection.

OBJECTIVES

A HCV avidity assay was evaluated for both plasma and DBS.

STUDY DESIGN

To measure antibody avidity a commercial HCV ELISA was modified using 7 M urea. The plasma samples were split into: group 1 (recently infected N = 19), group 2 (chronic carrier N = 300) and group 3 (resolved infection N = 82). Mock DBS made from group 1 (N = 12), group 2 (N = 50), group 3 (N = 25) and two seroconverter panels were evaluated. 133 DBS taken from patients known to have a resolved infection or be a chronic carrier were also tested.

RESULTS

The avidity assay cut-off was set at AI≤30 for a recent infection. Using sequential samples the assay could detect a recent infection in the first 4-5 months from the point of infection. Most of the false positive results (AI < 30 among cases known not to have had recent infection) were detected among known resolved infections, in both the plasma and DBS; as a result, a testing algorithm has been designed incorporating both PCR and two dilution factors. The sensitivity and specificity of the assay on plasma was 100% and 99.3%, respectively, while DBS had 100% sensitivity and 98.3% specificity.

CONCLUSION

The HCV avidity assay can be used to distinguish between chronic and recent infection using either plasma or DBS as the sample type.

Screening of lysosomal storage disorders: application of the online trapping-and-cleanup liquid chromatography/mass spectrometry method for mucopolysaccharidosis I

In recent years, new treatments have become available to treat some lysosomal storage disorders (LSDs) and many studies suggest that there is a benefit with starting therapy early. Newborn screening should detect diseases early enough for prompt treatment. Some countries include additional conditions, such as some LSDs, into their newborn screening panels. Mucopolysaccharidosis Type I (MPS I) is an autosomal recessive disorder caused by the deficiency of α-L-iduronidase (IDUA) activity. Currently, enzyme replacement therapy (ERT) or bone marrow transplantation is available and this has raised a growing interest for the development of a newborn screening test. In 2009, we reported a new fast and simplified tandem mass spectrometry-based method for quantifying five enzyme activities on dried blood spots. Here, we describe the inclusion of IDUA activity determination for the simultaneous detection of six lysosomal storage diseases. We have defined reference normal ranges by testing 680 healthy newborns and 240 adults. The assay was checked through three confirmed MPS I patients whose IDUA activity was below the normal range. Reproducibility of the assays has been established by assessing the intra-day and inter-day assay imprecisions. This quick assay has been devised to be implemented in newborn screening by liquid chromatography tandem mass spectrometry.

Ultramicro-fluorometric assay for the diagnosis of Gaucher disease in dried blood spots on filter paper

BACKGROUND

Gaucher disease (GD) is a lysosomal storage disorder characterized by a deficiency of the lysosomal acid β-D-glucosidase (GBA). The aim of this study was to develop an ultramicro-fluorometric assay based on the method of Chamoles et al. for determining GBA activity in dried blood spots on filter paper (DBS).

METHODS

The assay used 3-mm diameter blood spot and 8 mmol/l of 4-methylumbelliferyl-β-D-glucoside as enzymatic substrate. The reaction occurred in plates incubated at 37°C for 20 hours and the enzyme activity was expressed in μmol hydrolysed substrate/l blood/h. The fluorescence of the enzyme product was automatically measured in a fluorometer-photometer reader (SUMA Technology).

RESULTS

The intra and inter-assay coefficients of variation were lower than 9 and 12%, respectively, and the recovery range was 97-109%.Three patients with GD were correctly diagnosed using the ultramicroassay. Healthy newborn DBS samples (n = 3003) from the National Neonatal Screening Program were analyzed, and the mean GBA activity was 5.7 μmol/l blood/h. Our assay showed high Pearson (n = 26; r = 0.99) and concordance correlations (ρc = 0.99) with the traditional method described by Chamoles et al.

CONCLUSIONS

The analytical performance characteristics of our ultramicro-fluorometric assay suggest that it can be used in the diagnosis of GD in newborns and adults.

Extraction and analysis of carnitine and acylcarnitines by electrospray ionization tandem mass spectrometry directly from dried blood and plasma spots using a novel autosampler

RATIONALE

Acylcarnitines are routinely analyzed by electrospray ionization tandem mass spectrometry (ESI-MS/MS) both in clinical diagnostic and public health newborn screening laboratories from plasma and dried whole blood spots (DBS) on filter paper. The use of DBS as a convenient method of collecting and storing samples for subsequent analysis of various biomolecules is increasing, thus prompting the development of new devices to recover and quantify such analytes in an automated manner.

METHODS

Acylcarnitines were extracted directly from DBS using a novel autosampler that sequentially loads DBS cards into a pneumatic clamp and then pumps a fixed volume of solvent containing appropriate internal standards through a section of the DBS card directly into a triple quadrupole mass spectrometer via ESI. Plasma was first spiked with internal standard then spotted onto filter paper for analysis.

RESULTS

Acylcarnitines were analyzed in DBS, and both free and total carnitine were assayed in dried plasma spots (DPS). Results using the new autosampling technique were of equal quality to those obtained by punching a 3-mm diameter disk from a DBS or DPS, then extracting and analyzing the target analytes from conventional 96-well microtiter plates, with far reduced time per sample. Recovery for most analytes was >60% and reproducibility was generally within 20% (CV).

CONCLUSIONS

The simplicity and robustness of the DBS autosampler make it an attractive alternative to conventional methods of analyzing DBS specimens, thus saving time and labor costs, especially in high-throughput applications. Although the method as described is for direct infusion analysis, the autosampler is easily coupled to column hardware for applications requiring liquid chromatography/mass spectrometry (LC/MS).

Top-down proteomics and direct surface sampling of neonatal dried blood spots: diagnosis of unknown hemoglobin variants

We have previously shown that liquid microjunction surface sampling of dried blood spots coupled with high resolution top-down mass spectrometry may be used for screening of common hemoglobin variants HbS, HbC, and HbD. In order to test the robustness of the approach, we have applied the approach to unknown hemoglobin variants. Six neonatal dried blood spot samples that had been identified as variants, but which could not be diagnosed by current screening methods, were analyzed by direct surface sampling top-down mass spectrometry. Both collision-induced dissociation and electron transfer dissociation mass spectrometry were employed. Four of the samples were identified as β-chain variants: two were heterozygous Hb D-Iran, one was heterozygous Hb Headington, and one was heterozygous Hb J-Baltimore. The fifth sample was identified as the α-chain variant heterozygous Hb Phnom Penh. Analysis of the sixth sample suggested that it did not in fact contain a variant. Adoption of the approach in the clinic would require speed in both data collection and interpretation. To address that issue, we have compared manual data analysis with freely available data analysis software (ProsightPTM). The results demonstrate the power of top-down proteomics for hemoglobin variant analysis in newborn samples.

Short-incubation mass spectrometry assay for lysosomal storage disorders in newborn and high-risk population screening

The interest in early detection strategies for lysosomal storage disorders (LSDs) in newborns and high-risk population has increased in the last years due to the availability of novel treatment strategies coupled with the development of diagnostic techniques. We report the development of a short-incubation mass spectrometry-based protocol that allows the detection of Gaucher, Niemann-Pick A/B, Pompe, Fabry and mucopolysaccharidosis type I disease within 4h including sample preparation from dried blood spots. Optimized sample handling without the need of time-consuming offline preparations, such as liquid-liquid and solid-phase extraction, allows the simultaneous quantification of five lysosomal enzyme activities using a cassette of substrates and deuterated internal standards. Applying incubation times of 3h revealed in intra-day CV% values ranging from 4% to 11% for all five enzyme activities, respectively. In a first clinical evaluation, we tested 825 unaffected newborns and 16 patients with LSDs using a multiplexed, turbulent flow chromatography-ultra high performance liquid chromatography-tandem mass spectrometer assay. All affected patients were identified accurately and could be differentiated from non-affected newborns. In comparison to previously published two-day assays, which included an overnight incubation, this protocol enabled the detection of lysosomal enzyme activities from sample to first result within half a day.

A simple screening method for individuals at risk of developing type 1 diabetes: measurement of islet cell autoantibodies (GADA, IA-2A, and IAA) on dried capillary blood spots collected on filter paper

There is limited information regarding the use of dried capillary blood spots collected on a filter paper (FP) to test for islet cell antibodies. The aim of this study was to validate the use of dried capillary blood spots collected on a FP for the analysis of islet cell antibodies. FP eluates were tested using both single and combined assay for antibodies to glutamic acid decarboxylase (GADA) and/or to the protein tyrosine phosphatase like IA-2 (IA-2A), and a single assay for antibodies to insulin (IAA). The results were compared with those of serum assays. Ninety-one subjects were studied. Forty had Type 1 diabetes mellitus (T1DM) and 51 were first-degree relatives (FDR) of patients with T1DM. The GADA and IA-2A were measured by radio-binding assays, which utilize 35S-labeled GAD65 and IA-2. IAA was measured by a microtiter plate assay using 125I-labeled insulin. Twenty-six of those with T1DM (65%) and 5 of the FDRs (10%) had at least 1 positive test on the single serum assays. The FP combi-assay for GADA and IA-2A had 97.8% concordance rate when compared with serum single assays for GADA and IA-2A. The concordance rate for individual assays were 96.7% for GADA, and 100% for both IA-2A and IAA There was significant correlation of the antibody levels between FP and serum specimen for all 3 antibodies. We conclude that antibody screening performed using dried capillary blood spots collected on a FP correlates well with serum assays, and provides an easy alternative for population screening.