Dried blood spot analysis of creatinine with LC-MS/MS in addition to immunosuppressants analysis

Automated analyses of dried blood spots collected by volumetric microsampling devices

BACKGROUND

Dried blood spot (DBS) sampling on cellulose cards suffers from varying blood haematocrit levels and from chromatographic effects, which have a direct impact on quantitative DBS analyses. Commercial volumetric microsampling devices were, therefore, introduced to mitigate these effects, however, these devices are not compatible with automated DBS processing systems and must be processed manually.

RESULTS

Capillary electrophoresis (CE) instruments use fused-silica (FS) capillaries for precise and accurate liquid handling as well as for injection, separation, and quantitative analyses of liquid samples. These inherent features of an Agilent 7100 CE instrument were employed for the automated processing (elution and homogenization) of DBSs collected by hemaPEN® volumetric devices (2.74 μL of capillary blood per spot). The hemaPEN® samples were processed directly in CE vials by consecutive transfers of 56 μL of methanol and 14 μL of deionized water through the FS capillary in a sequence of 39 DBSs with repeatability of the liquid transfers better than 1.4 %. The resulting DBS eluates were homogenized by a quick air flush through the capillary and analyzed by the same capillary and CE instrument. Creatinine was selected as a clinically relevant model analyte and its endogenous concentrations in DBSs were determined by CE with capacitively coupled contactless conductivity detection (CE-C4D) in a background electrolyte solution consisting of 50 mM acetic acid and 0.1 % (v/v) Tween 20 (pH 3.0). The overall repeatability of the automated DBS processing and CE-C4D analyses of 39 DBSs was ≤7.1 % (peak areas) and ≤0.6 % (migration times), the calibration curve was linear in the 25-500 μM range (R2 = 0.9993) and covered all endogenous blood creatinine levels, the limit of detection was 5.0 μM, and sample throughput was >12 DBSs per hour. DBS ageing for 60 days and varying blood haematocrit levels (20-70 %) did not affect creatinine quantitative results (≤6.9 % for peak areas). Inter-capillary and inter-instrument repeatability was ≤7.7 % (peak areas) and ≤3.4 % (migration times) and demonstrated an excellent transferability of the proposed analytical concept among laboratories.

SIGNIFICANCE AND NOVELTY

This contribution is the first-ever report on the use of a single off-the-shelf analytical instrument for fully automated analyses of DBSs collected by commercial volumetric microsampling devices and holds great promise for future unmanned quantitative DBS analyses.

A Systematic Literature Review on the Use of Dried Biofluid Microsampling in Patients With Kidney Disease

BACKGROUND

Kidney disease is fairly unique due to the lack of symptoms associated with disease activity, and it is therefore dependent on biological monitoring. Dried biofluids, particularly dried capillary blood spots, are an accessible, easy-to-use technology that have seen increased utility in basic science research over the past decade. However, their use is yet to reach the kidney patient population clinically or in large-scale discovery science initiatives. The aim of this study was to systematically evaluate the existing literature surrounding the use of dried biofluids in kidney research.

METHODS

A systematic literature review was conducted using three search engines and a predefined search term strategy. Results were summarised according to the collection method, type of biofluid, application to kidney disease, cost, sample stability and patient acceptability.

RESULTS

In total, 404 studies were identified and 67 were eligible. In total, 34,739 patients were recruited to these studies with a skew towards male participants (> 73%). The majority of samples were blood, which was used either for monitoring anti-rejection immunosuppressive drug concentrations or for kidney function. Dried biofluids offered significant cost savings to the patient and healthcare service. The majority of patients preferred home microsampling when compared to conventional monitoring.

CONCLUSION

There is an unmet need in bringing dried microsampling technology to advance kidney disease despite its advantages. This technology provides an opportunity to upscale patient recruitment and longitudinal sampling, enhance vein preservation and overcome participation bias in research.

Dried blood spot analysis for the quantification of vancomycin and creatinine using liquid chromatography - tandem mass spectrometry: Method development and validation

BACKGROUND

Vancomycin is a widely used antibiotic for the treatment of gram-positive bacterial infections, especially for methicillin-resistant Staphylococcus aureus (MRSA) infections. Due to a small therapeutic range and large inter-patient variability, therapeutic drug monitoring (TDM) of vancomycin is required to minimize toxicity and maximize treatment efficacy. Venous blood sampling is mostly applied for TDM of vancomycin, although this widely used sampling method is more invasive compared to less painful alternatives, such as the dried blood spot (DBS) method, which can be performed at home.

METHOD

We developed an UPLC-MS/MS method for the quantification of vancomycin and creatinine in DBS. A fast sample preparation and short analysis run time of 5.2 min were applied, which makes this method highly suitable for clinical settings. Validation was performed according to international (FDA and EMA) guidelines.

RESULTS

The validated concentration range was found linear for creatinine from 41.8 µmol/L to 722 µmol/L and for vancomycin from 3.8 mg/L to 76.6 mg/L (r2 > 0.990) and the inaccuracies, imprecisions, hematocrit effects, and recoveries were < 15 % for both compounds. No significant carryover effect was observed.

CONCLUSION

Hence, we successfully validated a quantification method for the simultaneous determination of creatinine and vancomycin in DBS.

Automated High-Throughput Quantification of Phenyl-γ-valerolactones and Creatinine in Urine by Laser Diode Thermal Desorption

Quantification of nutritional biomarkers is crucial to accurately assess the dietary intake of different classes of (poly)phenols in large epidemiological studies. High-throughput analysis is mandatory to apply this methodology in large cohorts. However, the current validated methods to quantify (poly)phenols metabolites in biological fluids use ultra performance liquid chromatography (UPLC), leading to analysis time of several minutes per sample. To significantly reduce the run time, we developed and validated a method to quantify in urine the flavan-3-ols biomarkers, phenyl-γ-valerolactones (PVLs), using laser diode thermal desorption (LDTD). This mass spectrometry source allows direct introduction of sample extracts, resulting in analysis time of less than 10 s per sample. Also, to encompass the problem associated with the cost and availability of sulfated and glucuronide analytical standards, urine samples were subjected to enzymatic hydrolysis. Creatinine was also quantified to normalize the results obtained from the urinary spot. Results obtained with LDTD-MS/MS were cross-validated by UPLC-MS/MS using 155 urine samples. Coefficient of correlation was above 0.975 for PVLs and creatinine. For all analytes, the accuracy was between 90% and 113% by LDTD-MS/MS. Altogether, sample preparation was fully automated to demonstrate the application potential of this method to large cohorts.

Application of non-contact hematocrit prediction technologies to overcome hematocrit effects on immunosuppressant quantification from dried blood spots

Fully automated dried blood spot (DBS) analysis for therapeutic drug monitoring (TDM) of the immunosuppressants tacrolimus, sirolimus, everolimus and cyclosporin A suffers from a so-called hematocrit (hct) effect. This effect is related to the analysis of a partial DBS punch and extractability differences imposed by blood with different hcts. As this is intrinsic to automated DBS analysis, this poses a serious drawback for accurate immunosuppressant quantification. Knowledge of a sample's hct allows to correct the derived immunosuppressant concentrations for this effect. Unfortunately, when using the DBS approach for sampling at patients' homes, this hct will typically not be available. The aim of this study was to investigate the validity of a correction algorithm during fully automated DBS analysis of immunosuppressants, based on knowledge of the DBS' hct, obtained via two distinct non-contact hematocrit prediction strategies, using either near-infrared (NIR) or ultra-violet/visible (UV/VIS) spectroscopy. For tacrolimus, sirolimus, everolimus, and cyclosporin A, 48, 47, 58 and 48 paired venous whole blood and venous DBS patient samples were collected, respectively, and analyzed using an automated DBS-MS 500 HCT extraction unit coupled to a liquid chromatography tandem mass spectrometry system. Additionally, for all 201 samples the hct of the DBS was predicted based on NIR and UV/VIS spectroscopy. For tacrolimus and cyclosporin A, both hct prediction strategies allowed for adequate correction of the hct effect. Also for sirolimus and everolimus the results greatly improved after hct correction, although a hct bias remained for sirolimus and for everolimus a slightly significant hct effect was observed after NIR- and UV/VIS-based correction. Application of both hct prediction strategies ensured that clinical acceptance limits (i.e. ≥ 80% of the samples within 20% difference compared to whole blood) were met for all analytes. In conclusion, we demonstrated that non-contact hct prediction strategies, applied in tandem with fully automated DBS analysis, can be used to adequately correct immunosuppressant concentrations, yielding a good agreement with whole blood.

Liquid chromatography-tandem mass spectrometry for therapeutic drug monitoring of immunosuppressants and creatinine from a single dried blood spot using the Capitainer® qDBS device

In recent years, a lot of attention has been given to a more patient-centric therapeutic drug monitoring (TDM) of immunosuppressant drugs (tacrolimus, sirolimus, everolimus and cyclosporin A) by the use of microsampling techniques. By adopting Dried Blood Spots (DBS) after a finger prick, instead of conventional venous blood draws, follow-up can (partially) be established from patients' homes. Despite the many advantages of DBS, one of the major disadvantages associated with this technique is the well described hematocrit (hct) effect. In order to overcome the hct area bias, different strategies have been proposed, amongst which the use of dried blood sampling techniques based on the volumetric collection of blood. The aim of this study was to evaluate the use of the Capitainer® qDBS (quantitative Dried Blood Spot) device for the combined TDM of four immunosuppressants and creatinine from a single qDBS. The set-up of an adequate sample preparation allowing both immunosuppressants and creatinine quantification was one of the key challenges in the method development due to device-specific interferences. Liquid chromatography tandem-mass spectrometry methods for the quantification of tacrolimus, sirolimus, everolimus, cyclosporin A and creatinine from qDBS (10 μL) were developed and validated based on international guidelines, also taking into account DBS-specific parameters. The methods proved to be accurate and reproducible, with absolute biases below 10% and within-run CVs (%) below 8% over a calibration range from 1 to 50 ng/mL for tacrolimus, sirolimus and everolimus, 20-1500 ng/mL for cyclosporin A, and 15-700 μmol/L for creatinine. Reproducible (CV < 15%) IS-compensated relative recovery values were obtained, showing no hematocrit-dependence (compared to a hct of 0.37), except for cyclosporin A at higher hct values. Application on venous blood left-over patient samples showed good agreement between the results of Capitainer® qDBS and whole blood with 98% (47/48), 93% (41/44), 89% (41/46), 88% (38/43) and 89% (116/131) of the samples lying within 20% of the whole blood result for tacrolimus, sirolimus, everolimus, cyclosporin A and plasma/serum for creatinine, respectively. For creatinine a blood/plasma ratio of 0.85 was found and used to convert qDBS results to plasma/serum results. As a next step, capillary finger prick samples will need to demonstrate the clinical applicability of the method in a real life setting.

Dried blood microsampling-assisted therapeutic drug monitoring of immunosuppressants: An overview

In the field of solid organ transplantation, chemotherapy and autoimmune disorders, treatment with immunosuppressant drugs requires intensive follow-up of the blood concentrations via therapeutic drug monitoring (TDM) because of their narrow therapeutic window and high intra- and inter-subject variability. This requires frequent hospital visits and venepunctures to allow the determination of these analytes, putting a high burden on the patients. In the context of patient-centric thinking, it is becoming increasingly established that at least part of these conventional blood draws could be replaced by microsampling, allowing home-sampling and increasing the quality of life for these patients. In this review we discuss the published methods - mostly using liquid chromatography coupled to tandem mass spectrometry - that have utilized (volumetric) dried blood samples as an alternative for conventional liquid whole blood for the TDM of immunosuppressant drugs. Furthermore, some pre-analytical considerations using DBS or volumetric alternatives are considered, as well as the applicability on clinical samples. The implementation status in clinical practice is also discussed, including (1) the cost-effectiveness of this approach compared to venepuncture, (2) the availability of multiplexed methods, (3) the status of harmonization and (4) patient perception. A brief perspective on potential future developments for the dried blood-based TDM of immunosuppressant drugs is provided, by considering how obstacles for the implementation of these strategies into clinical practice might be overcome.

Analytical and clinical validation of Dried blood spot and Volumetric Absorptive Microsampling for measurement of tacrolimus and creatinine after renal transplantation

BACKGROUND

Serial monitoring of tacrolimus and serum creatinine after renal transplantation is of vital importance. In this study, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for the estimation of tacrolimus and creatinine, obtained from dried blood spots (DBS) or by volumetric absorptive microsampling (VAMS) was validated and the two sampling strategies were compared with traditional venous sampling.

METHODS

The LC-MS/MS assay was validated using a shared extract for the estimation of tacrolimus and creatinine from DBS and VAMS independently. The relationship between the concentrations in DBS/VAMS specimens and in venous samples was assessed using Passing-Bablok (PB) analysis and the bias between the two methods was determined by the Bland Altman (BA) analysis.

RESULTS

The imprecision and bias of tacrolimus and creatinine estimated from DBS and VAMS samples was <12% and was independent of the hematocrit (Hct). Samples were stable for five days at ambient temperature. From the PB regression analysis, correction equations were generated for the prediction of tacrolimus and creatinine values from DBS and VAMS samples. In a separate cohort of patients for validation, the corrected DBS and VAMS concentrations had a mean (95% CI) bias for tacrolimus of -0.64 (-2.98 to 1.70)% and -0.92 (-3.69 to 1.85)% respectively and for creatinine of 1.00 (-2.73 to 4.72)% and -0.71 (-3.74 to 2.32)% respectively. Using DBS and VAMS respectively, for tacrolimus, 91.8 and 89.8% of patient values and for creatinine, 69.4 and 81.6% of patient values were within the limits of clinical acceptance (within 15% agreement against the venous samples).

CONCLUSION

We conclude that VAMS is the preferred single sampling option for estimating tacrolimus and creatinine in renal transplant patients.

Validation of a dried blood spot method to measure tacrolimus concentrations in small volumes of mouse blood

Background: The small blood volume of mice complicates tacrolimus pharmacokinetic studies in these animals. Here we explored dried blood spot (DBS) as a novel method to measure tacrolimus blood concentrations in mice. DBS samples were collected from three sampling sites (cheek, tail and heart) and compared with heart whole blood samples measured via LC-MS/MS. Results: Tacrolimus concentrations in the whole blood samples ranged from 2.56 to 27.64 μg/l. DBS of cheek vein blood was the most reliable sampling site, with a mean bias of 0.15 μg/l (95% CI: -4.20 to 4.50). Conclusion: The DBS cheek method can be used for serial monitoring of tacrolimus blood concentrations in mice, offering an animal-friendly method for tacrolimus pharmacokinetic studies in mice.

Dried blood spots analysis of 6β-hydroxycortisol and cortisol using liquid chromatography/tandem mass spectrometry for calculating 6β-hydroxycortisol to cortisol ratio

Dried blood spot (DBS) sampling is a minimally invasive method used to collect blood samples of any population for personalized medicine. We aimed to develop a sensitive and reliable analytical method for measuring 6β-hydroxycortisol (6β-OHF) and cortisol concentrations in DBS by liquid chromatography/tandem mass spectrometry so as to utilize DBS as a less invasive blood sampling method for calculating the ratio of 6β-OHF/cortisol. The lower limits of quantification obtained using four DBS were 1.08 pg/50 μl for 6β-OHF and 1.01 pg/50 μl for cortisol. The 6β-OHF and cortisol in DBS were stable for 28 days at room temperature. The intraday and interday accuracy and precision of the method was <12%. Additionally, the 6β-OHF and cortisol in DBS were measured before, during, and after 3 days of clarithromycin administration to two of the subjects. Then, their concentration was compared in the plasma and whole blood collected simultaneously. The concentrations of 6β-OHF and cortisol in four DBS ranged from 0.007 to 0.079 ng/50 μl and from 1.15 to 6.66 ng/50 μl, respectively. The 6β-OHF/cortisol ratio in DBS decreased by approximately 50% on administering clarithromycin compared with that before the administration of clarithromycin. The 6β-OHF/cortisol ratio in DBS also showed a strong correlation with that in whole blood (r = 0.9694) and plasma (r = 0.9383). This method provides high accuracy and precision for measuring 6β-OHF and cortisol in DBS. It also allows the use of DBS instead of plasma for calculating the 6β-OHF/cortisol ratio. The 6β-OHF/cortisol ratio could be an index of CYP3A activity in clinical setting.

A comparison between two different dried blood substrates in determination of psychoactive substances in postmortem samples

Purpose

Whatman™ 903 cards represent a valid type of support for collection, storage, and analysis of dried blood spots (DBS). Whatman™ FTA (Flinders Technology Associates) are a type of cards soaked in chemicals that cause denaturation of proteins, while preserving DNA and ensuring the safe handling of DBS; to date, these cards are still rarely employed in forensic toxicology. The aim of this study was to analyze several psychoactive substances on not-dried blood on the two different cards and to compare the qualitative and quantitative results.

Methods

Twenty cardiac postmortem blood samples were collected and deposed on Whatman™ 903 and Whatman™ FTA cards. Spots and not-dried blood were analyzed following our validated and previously published liquid chromatography-mass spectrometry methods.

Results

We were able to identify: eight drugs of abuse and their metabolites (15 cases), five benzodiazepines and their metabolites (3 cases), six antidepressants (6 cases) and two antipsychotics (3 cases). We observed a perfect qualitative correspondence and a general good quantitative correlation between data obtained from not-dried blood and the two different DBS cards, except for alprazolam, diazepam, desmethyldiazepam, fluoxetine and sertraline, that showed a lower concentration on FTA. Additional experiments suggest that the chemicals, adsorbed on FTA, are not the cause of the loss of signal observed for the substances previously mentioned and that methanol should be preferred as extraction solvent.

Conclusions

This study proved that FTA cards are a good and a hazard-free alternative sample storage method for analysis of several psychoactive substances in postmortem blood.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11419-020-00567-2.

Validation of a simple liquid chromatography coupled to tandem mass spectrometry method for the simultaneous determination of tacrolimus, sirolimus, everolimus and cyclosporin A in dried matrix on paper discs

INTRODUCTION

Due to its high specificity and sensitivity, liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) is the gold standard method for immunosuppressant quantification in therapeutic drug monitoring. In this context, dried blood spots (DBS) have become a promising strategy as a sample collection procedure. Although the advantages of DBS over venipuncture are well known, this approach has limitations that strongly influence the acceptance of analytical results. Among them, the most important is hematocrit (Ht). The easiest way of overcoming this problem is by analyzing complete spots. In this strategy, called dried matrix on paper discs (DMPD), blood is volumetrically applied on pre-punched discs.

OBJECTIVES

To validate an LC-MS/MS method for the quantification of tacrolimus, sirolimus, everolimus and cyclosporin A using DMPD.

METHODS

The procedure was validated according to international guidelines using a commercial kit. The following performance parameters were evaluated: selectivity, carryover, linearity, accuracy, precision, lower limit of quantitation, relative recovery, commutability and stability. In addition, a method comparison study was performed to evaluate the clinical influence of Ht on the results.

RESULTS

All performance parameters were within acceptance criteria and, hence, it was determined that the validated method is fit for the intended purpose. Likewise, calculated bias values on medical decision levels showed that there was no clinical influence of Ht on the results.

CONCLUSION

Unlike other similar methodologies that have been published, here, a simple method has been fully validated. This is the first LC-MS/MS methodology adapting a commercial kit to use DMPD as a sampling strategy.

Assessment of tacrolimus and creatinine concentration collected using Mitra microsampling devices

Background

Current practice requires regular venous blood samples for monitoring of tacrolimus concentrations post renal transplant requiring regular hospital visits. Mitra devices use volumetric absorptive microsampling technology and absorb a fixed amount of blood (10  μL) from a capillary blood sample. They are a viable volumetric alternative to dried blood spots and are able to be posted to the laboratory for analysis.

Objective

The aim was to develop and validate liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays for tacrolimus and creatinine analysis using Mitra devices. The usefulness of this approach was assessed in renal transplant patients routinely monitored for tacrolimus and creatinine.

Method

Routine tacrolimus samples were used to assess the utility and reliability of Mitra sampling. Shared sample preparation for both tacrolimus and creatinine was carried out in a 96-deep well plate; mass spectrometric analysis was then undertaken for tacrolimus followed by re-injection for creatinine analysis.

Results

Comparison of 131 Mitra samples with a routine LC-MS/MS assay for tacrolimus showed a minimal bias –5.6% (95% CI –8.5 to –2.7%). Comparison of 135 serum and Mitra samples for creatinine using a fully validated LC-MS/MS assay showed a bias –6.5% (95% CI –8.5 to –4.5%).

Discussion

We have developed assays for tacrolimus and creatinine on fingerprick blood using the Mitra device and believe this approach provides a viable alternative to repeated venepuncture for therapeutic drug monitoring. This method could open up the opportunity for patients to perform tacrolimus and kidney function monitoring at home.

Emerging trends in paper spray mass spectrometry: Microsampling, storage, direct analysis, and applications

Recent advancements in the sensitivity of chemical instrumentation have led to increased interest in the use of microsamples for translational and biomedical research. Paper substrates are by far the most widely used media for biofluid collection, and mass spectrometry is the preferred method of analysis of the resultant dried blood spot (DBS) samples. Although there have been a variety of review papers published on DBS, there has been no attempt to unify the century old DBS methodology with modern applications utilizing modified paper and paper-based microfluidics for sampling, storage, processing, and analysis. This critical review will discuss how mass spectrometry has expanded the utility of paper substrates from sample collection and storage, to direct complex mixture analysis to on-surface reaction monitoring.

Volumetric absorptive microsampling and dried blood spot microsampling vs. conventional venous sampling for tacrolimus trough concentration monitoring

Objectives

Monitoring tacrolimus blood concentrations is important for preventing allograft rejection in transplant patients. Our hospital offers dried blood spot (DBS) sampling, giving patients the opportunity to sample a drop of blood from a fingerprick at home, which can be sent to the laboratory by mail. In this study, both a volumetric absorptive microsampling (VAMS) device and DBS sampling were compared to venous whole blood (WB) sampling.

Methods

A total of 130 matched fingerprick VAMS, fingerprick DBS and venous WB samples were obtained from 107 different kidney transplant patients by trained phlebotomists for method comparison using Passing-Bablok regression. Bias was assessed using Bland-Altman. A multidisciplinary team pre-defined an acceptance limit requiring >80% of all matched samples within 15% of the mean of both samples. Sampling quality was evaluated for both VAMS and DBS samples.

Results

32.3% of the VAMS samples and 6.2% of the DBS samples were of insufficient quality, leading to 88 matched samples fit for analysis. Passing-Bablok regression showed a significant difference between VAMS and WB, with a slope of 0.88 (95% CI 0.81–0.97) but not for DBS (slope 1.00; 95% CI 0.95–1.04). Both VAMS (after correction for the slope) and DBS showed no significant bias in Bland-Altman analysis. For VAMS and DBS, the acceptance limit was met for 83.0% and 96.6% of the samples, respectively.

Conclusions

VAMS sampling can replace WB sampling for tacrolimus trough concentration monitoring, but VAMS sampling is currently inferior to DBS sampling, both regarding sample quality and agreement with WB tacrolimus concentrations.

Hyphenated mass spectrometry techniques for assessing medication adherence: advantages, challenges, clinical applications and future perspectives

Nonadherence to prescribed pharmacotherapy is an understated public health problem globally and is costing many patients their chance to return to good health and healthcare systems billions. Clinicians need an accurate assessment of adherence to medications to aid the clinical decision-making process in the event of poor patient progress and to maximise the patient health outcomes from the drug therapies prescribed. An overview of indirect and direct methods used to measure medication adherence is presented, highlighting the potential for accurate measuring of drugs in biological samples using hyphenated mass spectrometry (MS) techniques to provide healthcare professionals with a reliable evidence base for clinical decision making. In this review we summarise published applications of hyphenated MS techniques for a diverse range of clinical areas demonstrating the rise in the use of such direct methods for assessing medication adherence. Although liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods using plasma, serum and urine samples are the most popular, in recent years increased attention has been given to liquid chromatography high-resolution mass spectrometry (LC-HRMS) methods and alternative biosample matrices including hair, saliva and blood microsamples. The advantages and challenges of using hyphenated MS techniques to address this healthcare problem are also discussed alongside future perspectives.

Official International Association for Therapeutic Drug Monitoring and Clinical Toxicology Guideline: Development and Validation of Dried Blood Spot-Based Methods for Therapeutic Drug Monitoring

Dried blood spot (DBS) analysis has been introduced more and more into clinical practice to facilitate Therapeutic Drug Monitoring (TDM). To assure the quality of bioanalytical methods, the design, development and validation needs to fit the intended use. Current validation requirements, described in guidelines for traditional matrices (blood, plasma, serum), do not cover all necessary aspects of method development, analytical- and clinical validation of DBS assays for TDM. Therefore, this guideline provides parameters required for the validation of quantitative determination of small molecule drugs in DBS using chromatographic methods, and to provide advice on how these can be assessed. In addition, guidance is given on the application of validated methods in a routine context. First, considerations for the method development stage are described covering sample collection procedure, type of filter paper and punch size, sample volume, drying and storage, internal standard incorporation, type of blood used, sample preparation and prevalidation. Second, common parameters regarding analytical validation are described in context of DBS analysis with the addition of DBS-specific parameters, such as volume-, volcano- and hematocrit effects. Third, clinical validation studies are described, including number of clinical samples and patients, comparison of DBS with venous blood, statistical methods and interpretation, spot quality, sampling procedure, duplicates, outliers, automated analysis methods and quality control programs. Lastly, cross-validation is discussed, covering changes made to existing sampling- and analysis methods. This guideline of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology on the development, validation and evaluation of DBS-based methods for the purpose of TDM aims to contribute to high-quality micro sampling methods used in clinical practice.

Effects, costs and implementation of monitoring kidney transplant patients' tacrolimus levels with dried blood spot sampling: A randomized controlled hybrid implementation trial

Aims

Dried blood spot (DBS) home sampling allows monitoring creatinine levels and tacrolimus trough levels as an alternative for blood sampling in the hospital, which is important in kidney transplant patient follow‐up. This study aims to assess whether DBS home sampling results in decreased patient travel burden and lower societal costs.

Methods

In this single‐centre randomized controlled hybrid implementation trial, adult kidney transplant patients were enrolled. The intervention group (n = 25) used DBS home sampling on top of usual care in the first 6 months after transplantation. The control group (n = 23) received usual care only. The primary endpoint was the number of outpatient visits. Other endpoints were costs per patient, patient satisfaction and implementation.

Results

There was no statistically significant difference in the average number of outpatient visits between the DBS group (11.2, standard deviation: 1.7) and the control group (10.9, standard deviation: 1.4; P = .48). Average costs per visit in the DBS group were not significantly different (€542, 95% confidence interval €316–990) compared to the control group (€533, 95% confidence interval €278–1093; P = .66). Most patients (n = 19/23, 82.6%) were willing to perform DBS home‐sampling if this would reduce the number of hospital visits. Only 55.9% (n = 143/256) of the expected DBS samples were received and 1/5 analysed on time (n = 52/256).

Conclusion

Adult kidney transplant patients are willing to perform DBS home sampling. However, to decrease patient travel burden and costs in post‐transplant care, optimization of the logistical process concerning mailing and analysis of DBS samples is crucial.

Vancomycin and creatinine determination in dried blood spots: Analytical validation and clinical assessment

This study aims to develop a liquid chromatography tandem-mass spectrometry (LC-MS/MS) method for vancomycin and creatinine measurement in dried blood spots (DBS) and to evaluate its clinical application. The analytes were extracted from DBS and analyzed by LC-MS/MS. Vancomycin and creatinine DBS and plasma concentrations were compared in 54 and 35 samples, respectively, from 29 patients. Accuracy was 94.4-102.6%, intra-assay precision was 2.1-5.6%, and inter-assay precision was 3.5-7.0%. Patients vancomycin plasma to DBS concentration ratios were highly variable (1.148-5.022), differently from creatinine (0.800-1.283). The assay has adequate analytical performance. Plasma concentrations can be satisfactorily predicted from DBS measurements for creatinine, but not for vancomycin, which limits its clinical application.

Dried blood spot testing for estimation of renal function and analysis of metformin and sitagliptin concentrations in diabetic patients: a cross-sectional study

PURPOSE

Dried blot spot (DBS) analysis of drugs or clinical parameters offers many advantages. We investigated the feasibility of using DBS for analysis of anti-diabetic drugs concomitantly with the estimated creatinine clearance (Cl_crea).

METHODS

The cross-sectional study involved physicians in an enabling analysis with 70 diabetic patients and community pharmacists in a field investigation with 84 participants. All 154 DBS samples were analyzed for creatinine, metformin, and sitagliptin.

RESULTS

The diabetic patients revealed of a wide range of age (32-88 years), BMI values (19.8-54.7 kg/m²), and extent of polypharmacotherapy (1-21 drugs). A correlation factor to convert capillary blood creatinine from DBS into plasma concentrations was determined. Patients' Cl_crea ranged from 21.6-155.9 mL/min. The results indicated statistically significant correlations (p < 0.05) between the use of two or three particular drug classes (diuretics, NSAIDs, renin-angiotensin system blockers) and a decreased renal function. DBS concentrations of metformin ranged between 0.23-4.99 μg/mL. The estimated elimination half-life (t ½) of metformin was 11.9 h in patients with a Cl_Crea higher than 60 mL/min and 18.5 h for diabetics with lower Cl_Crea. Sitagliptin capillary blood concentrations ranged between 11.12-995.6 ng/mL. Calculated t ½ of sitagliptin were 8.4 h and 13.0 h in patients with a Cl_Crea above and below 60 mL/min, respectively.

CONCLUSIONS

DBS allow for the analysis of concentrations of predominantly renally eliminated drugs and community pharmacists can provide a valuable contribution to DBS sampling.

Therapeutic drug monitoring of tacrolimus and mycophenolic acid in outpatient renal transplant recipients using a volumetric dried blood spot sampling device

AIMS

Tacrolimus and mycophenolic acid dosing after renal transplantation is individualized through therapeutic drug monitoring (TDM). Home-based dried blood spot (DBS) sampling has the potential to replace conventional TDM sampling at the clinic. A liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay was developed to quantify tacrolimus and mycophenolic acid in DBS and clinically validated for abbreviated area under the concentration-time curve (AUC) monitoring using an innovative volumetric DBS sampling device.

METHODS

Clinical validation was performed by direct comparison of paired DBS and whole blood (WB) (tacrolimus) and plasma (mycophenolic acid) concentrations and AUCs. Agreement was evaluated using Passing-Bablok regression, Bland-Altman analysis and DBS-to-WB predictive performance. TDM dosing recommendations based on both methods were compared to assess clinical impact.

RESULTS

Paired tacrolimus (n = 200) and mycophenolic acid (n = 192) DBS and WB samples were collected from 65 kidney(-pancreas) transplant recipients. Differences for tacrolimus and mycophenolic acid were within ±20% for 84.5% and 76.6% of concentrations and 90.5% and 90.7% of AUCs, respectively. Tacrolimus and mycophenolic acid dosing recommendation differences occurred on 44.4% and 4.7% of occasions. Tacrolimus DBS dosing recommendations were 0.35 ± 0.14 mg higher than for WB and 8 ± 3% of the initial dose. Mycophenolic acid DBS dosing recommendations were 23.3 ± 31.9 mg lower than for plasma and 2 ± 3.5% of the initial dose.

CONCLUSIONS

Tacrolimus and mycophenolic acid TDM for outpatient renal transplant recipients, based on abbreviated AUC collected with a DBS sampling device, is comparable to conventional TDM based on WB sampling. Patient training and guidance on good blood-spotting practices is essential to ensure method feasibility.

Pharmacokinetic considerations related to therapeutic drug monitoring of tacrolimus in kidney transplant patients

INTRODUCTION

Tacrolimus (Tac) is the cornerstone of immunosuppressive therapy after solid organ transplantation and will probably remain so. Excluding belatacept, no new immunosuppressive drugs were registered for the prevention of acute rejection during the last decade. For several immunosuppressive drugs, clinical development halted because they weren't sufficiently effective or more toxic. Areas covered: Current methods of monitoring Tac treatment, focusing on traditional therapeutic drug monitoring (TDM), controversies surrounding TDM, novel matrices, pharmacogenetic and pharmacodynamic monitoring are discussed. Expert opinion: Due to a narrow therapeutic index and large interpatient pharmacokinetic variability, TDM has been implemented for individualization of Tac dose to maintain drug efficacy and minimize the consequences of overexposure. The relationship between predose concentrations and the occurrence of rejection or toxicity is controversial. Acute cellular rejection also occurs when the Tac concentration is within the target range, suggesting that Tac whole blood concentrations don't necessarily correlate with pharmacological effect. Intracellular Tac, the unbound fraction of Tac or pharmacodynamic monitoring could be better biomarkers/tools for adequate Tac exposure - research into this has been promising. Traditional TDM, perhaps following pre-emptive genotyping for Tac-metabolizing enzymes, must suffice for a few years before these strategies can be implemented in clinical practice.

Longitudinal study on the use of dried blood spots for home monitoring in children after kidney transplantation

The use of DBSs for home monitoring has been limited due to unsatisfactory blood sampling and analytical difficulties. The aim of this longitudinal feasibility trial was to assess the utility of DBS to monitor TAC and Cr at home in transplant recipients. A total of 30 participants (2-21 years, mean±SD, 13.6±5.4 year) were enrolled over 12 months. Eighteen were males. Monthly DBS samples were obtained at home and mailed to the central laboratory for analysis of TAC and Cr. Nineteen patients completed the study, and 216 cards were received in the laboratory from a total of 279 cards expected, with 416/519 (80%) blood spots being suitable for analysis. We found a high correlation between blood TAC and Cr levels by DBS and the clinical laboratory, R² =.81 and .95, respectively. Fifteen parents and 15 youth completed measures of satisfaction with and preference for DBS testing. All but one parent/caregiver and youth reported satisfaction and preference for this method of testing over laboratory blood draws. We conclude that home DBS monitoring is a feasible method to monitor TAC and Cr in pediatric transplant recipients.

Dried blood spot validation of five immunosuppressants, without hematocrit correction, on two LC–MS/MS systems

Aim: Hematocrit (Ht) effects remain a challenge in dried blood spot (DBS) sampling. The aim was to develop an immunosuppressant DBS assay on two LC–MS/MS systems covering a clinically relevant Ht range without Ht correction. Results: The method was partially validated for tacrolimus, sirolimus, everolimus, cyclosporin A and fully validated for mycophenolic acid on an Agilent and Thermo LC–MS/MS system. Bias caused by Ht effects were within 15% for all immunosuppressants between Ht levels of 0.23 and 0.48 l/l. Clinical validation of DBS versus whole blood samples for tacrolimus and cyclosporin A showed no differences between the two matrices. Conclusion: A multiple immunosuppressant DBS method without Ht correction, has been validated, including a clinical validation for tacrolimus and cyclosporin A, making this procedure suitable for home sampling.

Dried Blood Spot sampling in psychiatry: Perspectives for improving therapeutic drug monitoring

Assessment of drug concentrations is indicated to guide dosing of a selected number of drugs used in psychiatry. Conventionally this is done by vena puncture. Novel sampling strategies such as dried blood spot (DBS) sampling have been developed for various drugs, including antipsychotics, antidepressants and mood-stabilizers. DBS sampling is typically performed by means of a finger prick. This method allows for remote sampling, which means that patients are not required to travel to a health care facility. The number of DBS assays for drugs used in psychiatry has increased over the last decade and includes antidepressants (tricyclic and serotonin and/or norepinephrine reuptake inhibitors), mood stabilizers and first- and second-generation antipsychotics. Available assays often comply with analytical validation criteria but are seldom used in routine clinical care. Little attention has been paid to the clinical validation and implementation processes of home sampling. Ideally, not only medicines but also clinical chemistry parameters should be measured within the same sample. This article reflects on the position of DBS remote sampling in psychiatry and provides insight in the requisites of making such a sampling tool successful.

Cost Evaluation of Dried Blood Spot Home Sampling as Compared to Conventional Sampling for Therapeutic Drug Monitoring in Children

Dried blood spot (DBS) sampling for the purpose of therapeutic drug monitoring can be an attractive alternative for conventional blood sampling, especially in children. This study aimed to compare all costs involved in conventional sampling versus DBS home sampling in two pediatric populations: renal transplant patients and hemato-oncology patients. Total costs were computed from a societal perspective by adding up healthcare cost, patient related costs and costs related to loss of productivity of the caregiver. Switching to DBS home sampling was associated with a cost reduction of 43% for hemato-oncology patients (€277 to €158) and 61% for nephrology patients (€259 to €102) from a societal perspective (total costs) per blood draw. From a healthcare perspective, costs reduced with 7% for hemato-oncology patients and with 21% for nephrology patients. Total savings depend on the number of hospital visits that can be avoided by using home sampling instead of conventional sampling.

A validated LC–MS/MS method for the quantitative measurement of creatinine as an endogenous biomarker in human plasma

Background: Creatinine is an endogenous compound generated from creatine by normal muscular metabolism. It is an important indicator of renal function and the serum level is routinely monitored in clinical labs. Results & methodology: Surrogate analyte (d3-creatinine) was used for calibration standard and quality control preparation and the relative instrument response ratio between creatinine and d3-creatinine was used to calculate the endogenous creatinine concentrations. Conclusion: A fit-for-purpose strategy of using a surrogate analyte and authentic matrix was adopted for this validation. The assay was the first human plasma assay using such strategy and was successfully applied to a clinical study to confirm a transient elevation of creatinine observed using an existing clinical assay.

LC-MS/MS Method for Serum Creatinine: Comparison with Enzymatic Method and Jaffe Method

Accurate quantification of creatinine (Cre) is important to estimate glomerular filtration rate (GFR). Differences among various methods of Cre quantification were previously noted. This study aims to develop a liquid chromatography tandem mass spectrometry (LC-MS/MS) method for serum Cre and compare this method with clinical routine methods. LC-MS/MS analysis was performed on API 4000 triple quadrupole mass spectrometer coupled with an Agilent 1200 liquid chromatography system. After adding isotope-labeled Cre-d3 as internal standard, serum samples were prepared via a one-step protein precipitation with methanol. The LC-MS/MS method was compared with frequently used enzymatic method and Jaffe method. This developed method, with a total run time of 3 min, had a lower limit of quantification of 4.4 μmol/L, a total imprecision of 1.15%–3.84%, and an average bias of 1.06%. No significant matrix effect, carryover, and interference were observed for the LC-MS/MS method. The reference intervals of serum Cre measured by LC-MS/MS assay were 41–79 μmol/L for adult women, and 46–101 μmol/L for adult men. Using LC-MS/MS as a reference, the enzymatic method showed an average bias of -2.1% and the Jaffe method showed a substantial average bias of 11.7%. Compared with the LC-MS/MS method, significant negative bias was observed for the enzymatic and Jaffe methods in hemolytic and lipimic samples. We developed a simple, specific, and accurate LC-MS/MS method to analyze serum Cre. Discordance existed among different methods.