Dried blood spot testing for seven steroids using liquid chromatography-tandem mass spectrometry with reference interval determination in the Korean population

Best Practice for Identification of Classical 21-Hydroxylase Deficiency Should Include 21 Deoxycortisol Analysis with Appropriate Isomeric Steroid Separation

There are mixed reports on the inclusion and use of 21 deoxycortisol (21DF) as the primary decision marker for classical 21-hydroxylase deficiency. We hypothesize that this may be due to insufficient recognition of the presence and chromatographic separation of isomeric steroids. The aim of this study was to determine the comparative utility of 21DF for screening and diagnosis of CAH due to classical 21-hydroxylase deficiency using a second-tier LC-MS/MS method that included the separation of isomeric steroids to 17OHP and 21DF. For each baby sample, one 3.2 mm dried blood spot was eluted in a methanolic solution containing isotopically matched internal standards. Data were interrogated by univariate and receiver operator characteristic analysis. Steroid profile results were generated for 924 non-CAH baby samples (median gestational age 37 weeks, range 22 to 43 weeks) and 17 babies with 21-hydroxylase deficiency. The ROC curves demonstrated 21DF to have the best sensitivity and specificity for the diagnosis of classical 21-hydroxylase deficiency with an AUC = 1.0. The heatmap showed the very strong correlation (r = 0.83) between 17OHP and 21DF. Our data support 21DF as a robust marker for CAH due to 21-hydroxylase deficiency. We recommend that 21DF be incorporated into routine newborn screening panels as part of the second-tier LC-MS/MS method, follow-up plasma steroid panels, and external quality assurance material.

The use of liquid chromatography-tandem mass spectrometry in newborn screening for congenital adrenal hyperplasia: improvements and future perspectives

Newborn screening for congenital adrenal hyperplasia using 17-hydroxyprogesterone by immunoassay remains controversial despite screening been available for almost 40 years. Screening is confounded by poor immunoassay specificity, fetal adrenal physiology, stress, and illness which can result in a large number of false positive screening tests. Screening programmes apply higher screening thresholds based on co-variates such as birthweight or gestational age but the false positive rate using immunoassay remains high. Mass spectrometry was first applied to newborn screening for congenital adrenal hyperplasia over 15 years ago. Elevated 17-hydroxprogesterone by immunoassay can be retested with a specific liquid chromatography tandem mass spectrometry assay that may include additional steroid markers. Laboratories register with quality assurance programme providers to ensure accurate steroid measurements. This has led to improvements in screening but there are additional costs and added laboratory workload. The search for novel steroid markers may inform further improvements to screening. Studies have shown that 11-oxygenated androgens are elevated in untreated patients and that the adrenal steroidogenesis backdoor pathway is more active in babies with congenital adrenal hyperplasia. There is continual interest in 21-deoxycortisol, a specific marker of 21-hydroxylase deficiency. The measurement of androgenic steroids and their precursors by liquid chromatography tandem mass spectrometry in bloodspots may inform improvements for screening, diagnosis, and treatment monitoring. In this review, we describe how liquid chromatography tandem mass spectrometry has improved newborn screening for congenital adrenal hyperplasia and explore how future developments may inform further improvements to screening and diagnosis.

Simultaneous measurement of 19 steroid hormones in dried blood spots using ultra-performance liquid chromatography-tandem mass spectrometry

A rapid and accurate ultra-performance liquid chromatography-tandem-mass spectrometry (UPLC-MS/MS) method was developed for the measurement of 19 steroid hormones in dried blood spots and to achieve the highly traceable analysis of steroid hormones in dried blood samples. In this method, a BEH C8 column and UPLC-MS/MS were used for the separation of the steroid hormones. The extraction process was simple and accurate. The distribution ranges of 19 steroid hormones in four healthy individuals (2 males and 2 females) were determined simultaneously by positive ionization mode (ESI⁺) and negative ionization mode (ESI^-) analysis, which were recorded by multiple reaction monitoring (MRM) modes. The linearity of the standard curves of 19 steroid hormones in dried blood spots was good, and the linear correlation coefficients R² were all ≥0.997. Meanwhile, the matrix effect of the method ranged from 87.1% to 131.3%. Across the analytical range, the inter-assay coefficient of variation (CV) was <12.07% and the intra-assay CV was <18.16%. The spiked recovery was >67.33%. The distribution ranges of 19 steroid hormones in four healthy individuals were in agreement with those in previous reports. A UPLC-MS/MS method for the simultaneous measurement of 19 steroid hormones in dried blood spots was developed to achieve traceable analysis of steroid hormones in dried blood samples.

Steroid Profiling for the Diagnosis of Congenital Adrenal Hyperplasia by Microbore Ultra-performance Liquid Chromatography-Tandem Mass Spectrometry

BACKGROUND

A rapid and accurate measurement approach for 17α-hydroxyprogesterone (17-OHP) and related steroids in amount/volume-limited clinic samples is of importance for precise newborn diagnosis of congenital adrenal hyperplasia (CAH) and its subtypes in clinic.

METHODS

Sixteen steroids (17-OHP, androstenedione, cortisol, tetrahydro-11-deoxycortisol, pregnenolone, progesterone, 11-deoxycorticosterone, corticosterone, 21-deoxycortisol, 11-deoxycortisol, dehydroepiandrosterone, testosterone, aldosterone, 17α-hydroxypregnenolone, dihydrotestosterone and 18-hydroxycorticosterone) were included in the panel of high-throughput microbore ultra-performance liquid chromatography-tandem mass spectrometry. Samples were collected from 126 normal subjects and 65 patients including different subtypes of CAH.

RESULTS

The method was validated with satisfactory analytical performance in linearity, repeatability, recovery and limit of detection. Reference intervals for 16 steroids were established by quantifying the level of steroids detected in normal infants. The applicability of the method was tested by differentiating steroid metabolic characteristics between normal infants and infants with CAH, as well as between infants with different CAH subtypes. The relevance of 17-OHP, 21-deoxycortisol, and 17-OHP/11-deoxycortisol for 21-hydroxylase deficiency screening was demonstrated. The level of 11-deoxycorticosterone, 11-deoxycortisol, progesterone and androstenedione can be used for the diagnosis of different rare subtypes of CAH.

CONCLUSION

This study provides a strategy for highly efficient steroid analysis of amount/volume-limited clinic samples and holds great potential for clinical diagnosis of CAH.

Steroid profile in dried blood spots by liquid chromatography tandem mass spectrometry: Application to newborn screening for congenital adrenal hyperplasia in China

BACKGROUND

Newborn screening for congenital adrenal hyperplasia (CAH) using 17-hydroxyprogesterone dissociation-enhanced, lanthanide fluorescence immunoassay (DELFIA) generates a large number of false-positive results. The present study aimed to improve the sensitivity of the CAH neonatal screening by including second-tier steroid profiling in dried blood spots (DBS) using liquid chromatography tandem mass spectrometry (LC-MS/MS).

METHODS

We developed and validated a LC-MS/MS method for simultaneous determination of six steroids in DBS, including androstenedione, testosterone, 17-hydroxyprogesterone, 11-deoxycortisol, 21-deoxycortisol, and cortisol. Two 5-mm blood spots were eluted by internal standard working solution. We analyzed 1170 DBS samples from neonates to determine gestational age-specific reference intervals. In order to test the specificity of the second-tier method, we analyzed 707 cards with a positive screening by DELFIA.

RESULTS

Values of intra- and inter-day precision coefficients of variance and accuracy were 2.0%-13.3% and 85.8%-114.5%, respectively. Recovery ranged from 85.0% to 106.9%. The lower limit of quantification was 0.5 ng/mL for 21-deoxycortisol, 0.25 ng/mL for 17-hydroxyprogesterone and cortisol, and 0.1 ng/mL for testosterone, androstenedione, and 11-deoxycortisol. In addition, the linearity range was 0.25-50 ng/mL (R² > 0.99). According to the 17-hydroxyprogesterone levels and ratios of (androstenedione + 17-hydroxyprogesterone)/cortisol in the 707 positive screening samples, 77 neonates should receive recall visit. The number of false-positive results reduced by 89.1%. Totally, 18 newborns were diagnosed with 21-hydroxylase deficiency, one with P450 oxidoreductase deficiency and one with 11β-hydroxylase deficiency. With two-tier screening, the positive predictive value increased to 26.0%.

CONCLUSIONS

The second-tier steroid profiling by LC-MS/MS reduced the false-positive rate and improved the positive predictive value of CAH screening. We suggest applying this steroid profiling assay as a second-tier test for CAH screening in China.

Congenital Adrenal Hyperplasia-Current Insights in Pathophysiology, Diagnostics, and Management

Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders affecting cortisol biosynthesis. Reduced activity of an enzyme required for cortisol production leads to chronic overstimulation of the adrenal cortex and accumulation of precursors proximal to the blocked enzymatic step. The most common form of CAH is caused by steroid 21-hydroxylase deficiency due to mutations in CYP21A2. Since the last publication summarizing CAH in Endocrine Reviews in 2000, there have been numerous new developments. These include more detailed understanding of steroidogenic pathways, refinements in neonatal screening, improved diagnostic measurements utilizing chromatography and mass spectrometry coupled with steroid profiling, and improved genotyping methods. Clinical trials of alternative medications and modes of delivery have been recently completed or are under way. Genetic and cell-based treatments are being explored. A large body of data concerning long-term outcomes in patients affected by CAH, including psychosexual well-being, has been enhanced by the establishment of disease registries. This review provides the reader with current insights in CAH with special attention to these new developments.

Solutions for hematocrit bias in dried blood spot hormone analysis

Over the last years, dried blood spot (DBS) sampling has gained significant interest due to development of analytical techniques combined with DBS, the simplicity and low cost of the method. Despite its wide use, DBS sampling can lead to inaccurate results due to the impact of the hematocrit (Hct) on the analysis. Some analytes have shown to be hardly impacted by Hct values. However, in other cases, a significant impact of Hct is observed, which requires the use of alternative approaches to circumvent this issue. This review describes the possible impact of Hct-related bias in DBS sampling in the context of hormone analysis and discusses the different methodologies that can be used to overcome this bias to ensure accurate results.

Establishment of Pediatric Reference Intervals for Routine Laboratory Tests in Korean Population: A Retrospective Multicenter Analysis

Background

Reference intervals defined for adults or children of other ethnicities cannot be applied in the evaluation of Korean pediatric patients. Pediatric reference intervals are difficult to establish because children are in their growing stage and their physiology changes continuously. We aimed to establish reference intervals for routine laboratory tests for Korean pediatric patients through retrospective multicenter data analysis.

Methods

Preoperative laboratory test results from 1,031 pediatric patients aged 0 month–18 years who underwent minor surgeries in four university hospitals were collected. Age- and sex-specific reference intervals for routine laboratory tests were defined based on the Clinical and Laboratory Standards Institute (CLSI) EP28-A3c guidelines.

Results

The pediatric reference intervals determined in this study were different from existing adult reference intervals and pediatric reference intervals for other ethnicities. Most tests required age-specific partitioning, and some of those required sex-specific partitioning for at least one age-partitioned subgroup. Erythrocyte sedimentation rate, monocyte percentage, basophil percentage, activated partial thromboplastin time, glucose, cholesterol, albumin, bilirubin, chloride, and C-reactive protein did not show any difference between age- or sex-partitioned subgroups.

Conclusions

We determined Korean pediatric reference intervals for hematology, coagulation, and chemistry tests by indirect sampling based on medical record data from multiple institutions. These reference intervals would be valuable for clinical evaluations in the Korean pediatric population.

A validated surrogate analyte LC-MS/MS assay for quantification of endogenous cortisol in human whole blood

Cortisol is a steroid hormone that is frequently measured as a marker of stress, inflammation, and immune function. While commonly analyzed in saliva, hair, blood plasma and urine, a recent trend towards whole blood-based at-home collection devices has emerged, which necessitates development of more sensitive assays for cortisol in whole blood. To support the implementation of a patient-centric sampling approach in a drug development program, a fit-for-purpose surrogate analyte-based liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for cortisol in whole blood was developed using ¹³C₃-cortisol as a surrogate analyte and cortisol-d6 as the internal standard. The surrogate analyte approach was chosen due to a lack of available cortisol-free whole blood and the absence of appropriately representative surrogate matrices. Samples were prepared using supported liquid extraction, and the LC-MS/MS analysis consisted of a 4.00 min analytical run. The method demonstrated linearity between 0.500 and 500 ng/mL of ¹³C₃-cortisol, and accuracy, precision and robustness were all acceptable per current regulatory guidance for bioanalytical method validation of chromatographic assays for cortisol- and ¹³C₃-cortisol-based quality control (QC) samples when quantified against a ¹³C₃-cortisol calibration curve. The acceptable robustness of cortisol-based QCs when quantified against a ¹³C₃-cortisol-based calibration curve also suggests parallelism between the analytes. These results indicate a viable surrogate analyte method, that is fit-for-purpose to analyze whole blood cortisol levels using a surrogate analyte LC-MS/MS approach. Evaluation of patient samples showed very promising comparability between whole blood and plasma cortisol concentrations, suggesting that whole blood could be used in place of or in addition to a plasma-based sampling protocol in clinical trials analyzing cortisol. Overall, this method presents a novel tool that is a first step in supporting the trend towards sample miniaturization and at-home sample collection, and may be readily used in clinical and diagnostic settings.

How and when to use dried blood spots in psychoneuroendocrinological research

OBJECTIVE

The term "dried blood spot" (DBS) refers to a sampling technique in which capillary whole blood is spotted on filter paper. Given the possibility to determine a wide range of hormones and related biomarkers in DBS, the method should be of interest to researchers in psychoneuroendocrinology. So far, however, the how and when of using DBS in this context have not been outlined.

METHODS

A review of the literature was conducted in order to describe the materials and procedures necessary to determine relevant biological markers from DBS (how to use DBS). In addition, a comparison of the DBS method with other sampling techniques was undertaken and examples of its previous use in psychoneuroendocrinology were provided (when to use DBS).

RESULTS

Both dyadic and DBS self-sampling are feasible, and a number of protocols are available to determine endocrine and immune, genetic and epigenetic markers. Decisions to use DBS instead of venous blood or saliva sampling should mainly be guided by whether it is sensible and feasible to determine the parameter of interest in whole blood obtained from DBS. In addition, DBS are well suited for large study populations with specific vulnerabilities, and for remotely located studies with budgetary constraints.

CONCLUSION

Dried blood spots are a promising material as well as a simple sampling technique for psychoneuroendocrinological research. Future efforts should be directed at continuing to adapt existing serum and plasma analysis protocols for use with DBS, and at testing the feasibility of DBS self-sampling in field studies.

Dried Blood Spot Multiplexed Steroid Profiling Using Liquid Chromatography Tandem Mass Spectrometry in Korean Neonates

Background

Screening for congenital adrenal hyperplasia (CAH) using immunoassays for 17α-hydroxyprogesterone generates many false-positive results. We developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for simultaneous quantification of nine steroid hormones in dried blood spot (DBS) samples, and established reference intervals for these hormones.

Methods

We examined our method for linearity, precision, accuracy, extraction recovery, and matrix effects and determined the reference intervals of cortisol, 17α-hydroxyproges-terone, 11-deoxycortisol, 21-deoxycortisol, androstenedione, corticosterone, 11-deoxycorticosterone, testosterone, and progesterone in 1,146 DBS samples (from 272 preterm and 874 full-term neonates). Immunoassay and LC-MS/MS methods were compared for 17α-hydroxyprogesterone. Fourteen additional samples were tested to validate the clinical applicability of the LC-MS/MS method.

Results

The linearity range was 2.8–828.0 nmol/L for cortisol and 0.9–40.0 nmol/L for the other steroids (R²>0.99). Intra-day and inter-day precision CVs were 2.52–12.26% and 3.53–17.12%, respectively. Accuracy was 80.81–99.94%, and extraction recovery and matrix effects were 88.0–125.4% and 61.7–74.2%, respectively. There was a negative bias, with higher values measured by immunoassay compared with LC-MS/MS (r=0.8104, P<0.0001). The LC-MS/MS method was successfully applied to the analysis of nine steroids in DBS for screening and diagnosis of CAH using the 14 additional samples.

Conclusions

Our method enables highly sensitive and specific assessment of nine steroids from DBS and is a promising tool for clinical analysis of CAH.

Measurement of serum steroid profiles by HPLC-tandem mass spectrometry

Accurate investigations of adrenal hormone levels play a vital role in pediatric endocrinology for the detection of steroid-related disorders. In this study, we developed and validated a simultaneous assay for eight serum steroids, i.e., DHEA, androstenedione, testosterone, progesterone, 17‑hydroxyprogesterone, DHEA‑sulfate, pregnenolone‑sulfate and cholesterol-sulfate, using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Serum samples were prepared by liquid-liquid extraction with methyl t‑butyl ether. Quantitation by LC-MS/MS was performed in multiple reaction monitoring mode with an electrospray ionization source. The run time was 10 min. Analytical performance was evaluated, including imprecision, linearity, ion suppression, carry over and detection capabilities. Serum specimens from 59 children and 120 adults were analyzed to compare the distribution of steroid levels between the groups. All hormones were effectively extracted and separated using our method. The method was essentially free from potential interference and ion suppression. Within-run and between-run imprecision values were <20%. The lower limits of quantification varied from 0.025 to 10 ng/mL. The results were generally good and correlated with those obtained using immunoassay techniques. We developed the HPLC-MS/MS method for the simultaneous measurement of free and sulfated steroid hormones. The performance of the developed method was generally acceptable. Thus, this method may provide a novel approach to steroid profiling in children of age before adrenarche.

Neonatal Screening for Congenital Adrenal Hyperplasia in Turkey: A Pilot Study with 38,935 Infants

Objective

Congenital adrenal hyperplasia (CAH) is the most common form of primary adrenal insufficiency in children. Neonatal screening for CAH is effective in detecting the salt-wasting (SW) form and in reducing mortality. In this study, our aim was to estimate the incidence of CAH in Turkey and to assess the characteristics and efficacy of the adopted newborn CAH screening strategy.

Methods

A pilot newborn CAH screening study was carried out under the authority of the Turkish Directorate of Public Health. Newborn babies of ≥32 gestational weeks and ≥1500 gr birth weight from four cities, born between March 27-September 15, 2017 were included in the study. Screening protocol included one sample two-tier testing. In the first step, 17α-hydroxyprogesterone (17-OHP) was measured by fluoroimmunoassay in dried blood spots (DBS) obtained at 3-5 days of life. The cases with positive initial screening were tested by steroid profiling in DBS using a liquid chromatography-tandem mass spectrometry method to measure 17-OHP, 21-deoxycortisol (21-S), cortisol (F), 11-deoxycortisol and androstenedione as a second-tier test. The babies with a steroid ratio (21-S+17-OHP)/F of ≥0.5 were referred to pediatric endocrinology clinics for diagnostic assessment.

Results

38,935 infants were tested, 2265 (5.82%) required second-tier testing and 212 (0.54%) were referred for clinical assessment, six of whom were diagnosed with CAH (four males, two females). Four cases were identified as SW 21-hydroxylase deficiency (21-OHD) (two males, two females). One male baby had simple virilizing 21-OHD and one male baby had 11-OHD CAH. The incidence of classical 21-OHD in the screened population was 1:7,787.

Conclusion

The incidence of CAH due to classical 21-OHD is higher in Turkey compared to previous reports. We, therefore, suggest that CAH be added to the newborn screening panel in Turkey. The use of steroid profiling as a second-tier test was found to improve the efficacy of the screening and reduce the number of false-positives.

The evolution of methods for urinary steroid metabolomics in clinical investigations particularly in childhood

The metabolites of cortisol, and the intermediates in the pathways from cholesterol to cortisol and the adrenal sex steroids can be analysed in a single separation of steroids by gas chromatography (GC) coupled to MS to give a urinary steroid profile (USP). Steroids individually and in profile are now commonly measured in plasma by liquid chromatography (LC) coupled with MS/MS. The steroid conjugates in urine can be determined after hydrolysis and derivative formation and for the first time without hydrolysis using GC-MS, GC-MS/MS and liquid chromatography with mass spectrometry (LC-MS/MS). The evolution of the technology, practicalities and clinical applications are examined in this review. The patterns and quantities of steroids changes through childhood. Information can be obtained on production rates, from which children with steroid excess and deficiency states can be recognised when presenting with obesity, adrenarche, adrenal suppression, hypertension, adrenal tumours, intersex condition and early puberty, as examples. Genetic defects in steroid production and action can be detected by abnormalities from the GC-MS of steroids in urine. New mechanisms of steroid synthesis and metabolism have been recognised through steroid profiling. GC with tandem mass spectrometry (GC-MS/MS) has been used for the tentative identification of unknown steroids in urine from newborn infants with congenital adrenal hyperplasia. Suggestions are made as to areas for future research and for future applications of steroid profiling. As routine hospital laboratories become more familiar with the problems of chromatographic and MS analysis they can consider steroid profiling in their test repertoire although with LC-MS/MS of urinary steroids this is unlikely to become a routine test because of the availability, cost and purity of the internal standards and the complexity of data interpretation. Steroid profiling with quantitative analysis by mass spectrometry (MS) after chromatography now provides the most versatile of tests of adrenal function in childhood.

An untargeted metabolomics method for archived newborn dried blood spots in epidemiologic studies

INTRODUCTION

For pediatric diseases like childhood leukemia, a short latency period points to in-utero exposures as potentially important risk factors. Untargeted metabolomics of small molecules in archived newborn dried blood spots (DBS) offers an avenue for discovering early-life exposures that contribute to disease risks.

OBJECTIVES

The purpose of this study was to develop a quantitative method for untargeted analysis of archived newborn DBS for use in an epidemiological study (California Childhood Leukemia Study, CCLS).

METHODS

Using experimental DBS from the blood of an adult volunteer, we optimized extraction of small molecules and integrated measurement of potassium as a proxy for blood hematocrit. We then applied this extraction method to 4.7-mm punches from 106 control DBS samples from the CCLS. Sample extracts were analyzed with liquid chromatography high resolution mass spectrometry (LC-HRMS) and an untargeted workflow was used to screen for metabolites that discriminate population characteristics such as sex, ethnicity, and birth weight.

RESULTS

Thousands of small molecules were measured in extracts of archived DBS. Normalizing for potassium levels removed variability related to varying hematocrit across DBS punches. Of the roughly 1,000 prevalent small molecules that were tested, multivariate linear regression detected significant associations with ethnicity (3 metabolites) and birth weight (15 metabolites) after adjusting for multiple testing.

CONCLUSIONS

This untargeted workflow can be used for analysis of small molecules in archived DBS to discover novel biomarkers, to provide insights into the initiation and progression of diseases, and to provide guidance for disease prevention.

Multiplex Assay of Second-Line Anti-Tuberculosis Drugs in Dried Blood Spots Using Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry

As dried blood spots (DBSs) have various advantages over conventional venous blood sampling, some assays for detection of one or two anti-tuberculosis (TB) drugs in DBSs have been developed. However, there are no assays currently available for the simultaneous measurement of three or more anti-TB drugs in DBSs. In this study, we developed and evaluated a multiplex method for detecting nine anti-TB drugs including streptomycin, kanamycin, clarithromycin, cycloserine, moxifloxacin, levofloxacin, para-aminosalicylic acid, prothionamide, and linezolid in DBSs by using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Seventy-nine patient samples of DBS were analyzed on the UPLC-MS/MS system. All drug concentrations were determined within 4 min, and assay performance was evaluated. All drugs were clearly separated without ion suppression. Within-run and between-run precisions were 1.7-13.0% and 5.7-17.0%, respectively, at concentrations representing low and high levels for the nine drugs. Lower limits of detection and quantification were 0.06-0.6 and 0.5-5.0 µg/mL, respectively. Linearity was acceptable at five level concentrations for each drug. Correlations between drug concentrations in plasma and DBSs by using Passing-Bablock regression and Pearson's rho (ρ, 0.798-0.989) were acceptable. In conclusion, we developed a multiplex assay to measure nine second-line anti-TB drugs in DBSs successfully. This assay provided convenient and rapid drug quantification and could have applications in drug monitoring during treatment.

Advantages and Challenges of Dried Blood Spot Analysis by Mass Spectrometry Across the Total Testing Process

INTRODUCTION

Through the introduction of advanced analytical techniques and improved throughput, the scope of dried blood spot testing utilising mass spectrometric methods, has broadly expanded. Clinicians and researchers have become very enthusiastic about the potential applications of dried blood spot based mass spectrometric applications. Analysts on the other hand face challenges of sensitivity, reproducibility and overall accuracy of dried blood spot quantification. In this review, we aim to bring together these two facets to discuss the advantages and current challenges of non-newborn screening applications of dried blood spot quantification by mass spectrometry.

METHODS

To address these aims we performed a key word search of the PubMed and MEDLINE online databases in conjunction with individual manual searches to gather information. Keywords for the initial search included; "blood spot" and "mass spectrometry"; while excluding "newborn"; and "neonate". In addition, databases were restricted to English language and human specific. There was no time period limit applied.

RESULTS

As a result of these selection criteria, 194 references were identified for review. For presentation, this information is divided into: 1) clinical applications; and 2) analytical considerations across the total testing process; being pre-analytical, analytical and post-analytical considerations.

CONCLUSIONS

DBS analysis using MS applications is now broadly applied, with drug monitoring for both therapeutic and toxicological analysis being the most extensively reported. Several parameters can affect the accuracy of DBS measurement and further bridge experiments are required to develop adjustment rules for comparability between dried blood spot measures and the equivalent serum/plasma values. Likewise, the establishment of independent reference intervals for dried blood spot sample matrix is required.