Simultaneous determination of phenylalanine and tyrosine levels in human blood obtained by the dried spot technique for monitoring of patients with phenylketonuria

Monitoring patients with phenylketonuria (PKU) requires accurately measuring phenylalanine and tyrosine levels in a small volume of blood samples obtained by the dried blood spot (DBS) technique. The aim was to study selected parameters influencing the quantitative results. Phenylalanine and tyrosine were extracted from DBS samples with methanol, and 5 internal standard introduction techniques were tested. Phenylalanine and tyrosine levels were measured in 6-mm discs punched from DBS, pre-punched 9-mm discs containing the entire DBS sample, and liquid blood by HPLC-MS-MS. Levels in 6-mm discs punched from DBS measured by HPLC-MS/MS were compared with those measured by the HPLC-FLD. The analytical parameters of the method are satisfactory, linearity in the range of 25-1200 μmol/L (LOD, LOQ and LLOQ values 0.2 μmol/L, 0.5 μmol/L and 3.8 μmol/L for phenylalanine, 0.5 μmol/L, 1.5 μmol/L and 5.1 μmol/L for tyrosine), within-run precision 1.8 %-3.7 % for phenylalanine, 1.9 %-2.7 % for tyrosine, between-run precision 4.7 %-5.9 % for phenylalanine, 4.1 %-5.4 % for tyrosine, recovery 93.8 %-100.4 % for phenylalanine and 93.7 %-99.1 % for tyrosine. Good agreement was found between phenylalanine and tyrosine concentrations in 6-mm discs punched from DBS (R = 0.896, p < 0.001, and R = 0.907, p < 0.001, respectively), pre-punched 9-mm discs containing the entire DBS sample (R = 0.960, p < 0.001, and R = 0.950, p < 0.001, respectively) and liquid blood, as well as between phenylalanine and tyrosine concentrations obtained by HPLC-MS/MS and HPLC-FLD (R = 0.968, p < 0.001, and R = 0.984, p < 0.001, respectively). The presented method is suitable for monitoring patients with PKU.

Steroid hormone concentrations in dried blood spots: A comparison between capillary and venous blood samples

BACKGROUND

An important aspect of the shift towards dried blood spots (DBS) as a sample matrix for laboratory measurements, is the availability of robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods that can reliably quantify analyte concentrations in DBS. The development and validation of these LC-MS/MS methods, however, concerns an extensive process, for which large amounts of DBS samples are required. DBS are usually obtained from capillary blood samples, but they can also be prepared from venous (residual) blood samples, which are widely available in clinical laboratories. Therefore, we aimed to determine whether DBS prepared from (residual) venous blood samples, collected in EDTA blood tubes, can be used for future development and validation of LC-MS/MS methods to quantify steroid hormones in DBS.

METHODS

Capillary DBS and venous blood samples (EDTA tube and tube without additives) were collected from twenty healthy volunteers (12F/8M). From both venous blood samples, DBS were prepared volumetrically. Samples were analyzed using in-house developed LC-MS/MS methods for testosterone, androstenedione, 17-hydroxyprogesterone (17-OHP), cortisol, cortisone, corticosterone, and for dehydroepiandrosterone sulfate (DHEA-S).

RESULTS

DBS made from venous blood collected in EDTA tubes compared with capillary blood showed a correlation coefficient of ≥ 0.89 for all steroid hormones except corticosterone (0.67). DBS made from venous blood collected in tubes without additives showed a strong correlation with both DBS made from venous blood collected in EDTA tubes (≥0.97 for all steroid hormones) and capillary DBS (>0.90) except corticosterone (0.64).

CONCLUSION

DBS prepared from (residual) venous blood collected in EDTA blood tubes can be used for future development and validation of LC-MS/MS methods to quantify steroid hormones, except for corticosterone, in capillary DBS.

A comprehensive approach for detection of biotin deficiency from dried blood spot samples using liquid chromatography-mass spectrometry

Aim: The aim of the present study is to develop a liquid chromatography-mass spectrometry method to measure two important biomarkers of biotin deficiency from dried blood spot samples for effective management of the disorder. Materials & methods: The method was developed on a liquid chromatography-mass spectrometry system using pentafluorophenyl column employing a mobile phase composition of methanol and water in the isocratic mode. A full validation of the method was performed as per relevant guidelines. Results & conclusion: Correlation between the results of dried blood spot and plasma method was evaluated to determine the interconvertibility of the method. The developed method was successfully applied for establishing the reference ranges for these biomarkers in the population of Udupi, a coastal district of South India.

Stability of steroid hormones in dried blood spots (DBS)

OBJECTIVES

Steroid hormone levels of patients may be monitored via dried blood spot (DBS) sampling at home. Stability of steroid hormones in DBS samples, however, needs to be established.

METHODS

DBS samples from healthy volunteers were collected and stored at various temperatures. Steroid hormone concentrations in DBS were measured directly, at day 2, day 7 and day 14 following storage at 37 °C and after 7 days, 14 days, 3 months and 6 months following storage at -20 °C, 4 °C and room temperature (RT). Cortisol, cortisone, corticosterone, testosterone, androstenedione, and 17-hydroxyprogesterone (17-OHP) were assessed using LC-MS/MS.

RESULTS

All steroids were stable (±15 %) up to 14 days when stored at 37 °C, except for cortisone (only stable until 2 days). All steroids were stable up to 6 months when stored at -20 °C, 4 °C and RT. However, there were some exceptions, for androstenedione at RT (only stable until 7 days), for 17-OHP when stored at -20 °C (only stable until 3 months), for cortisone at RT and 4 °C (only stable until 14 days), and cortisol at RT (only stable until 3 months).

CONCLUSIONS

Overall, we demonstrated stability of steroid hormone concentrations in DBS under various conditions which may be encountered during shipping to the diagnostic laboratory and during long-term storage before analysis.

Liquid chromatography-mass spectrometric method for the simultaneous analysis of branched-chain amino acids and their ketoacids from dried blood spot as secondary analytes for the detection of maple syrup urine disease

Background

Maple syrup urine disease (MSUD) is an aminoacidopathy caused by a defective branched-chain alpha-ketoacid dehydrogenase complex, leading to the accumulation of branched-chain amino acids (BCAAs) and their respective keto acids (BCKAs). A comprehensive test was developed to measure BCAAs and BCKAs using LC-MS from dried blood spot (DBS) samples for the diagnosis and prevention of MSUD in newborns and infants.

Methods

Analytes were extracted from DBS using a methanol:0.1 % v/v formic acid solution (75:25) containing internal standards and analyzed on a Luna PFP column (150 mm × 4.6 mm, 3 µm) at a flow rate of 0.3 mL/min. The method was validated for linearity, accuracy, precision, recovery, carry-over, matrix effect, hematocrit, blood volume, and punch position effects. Biomarker stability in the matrix and stock solution was assessed. Correlation with the plasma method was determined using Pearson's correlation coefficient and Bland-Altman analysis. The method established reference ranges for the Udupi district population in South India.

Results

The method demonstrated linearity (r2 > 0.99), with a lower limit of detection at 2 µM (BCAA) and 1 µM (BCKA), and acceptable recovery of QC samples. Hematocrit, blood volume, punch position, and storage condition effects were within acceptable limits. Correlation and Bland-Altman analysis showed strong interconvertibility between plasma and DBS assays. Reference ranges for leucine, isoleucine, valine, KIC, KIV, and KMV were established.

Conclusion

The developed DBS method, requiring no derivatization and involving simple sample preparation with short run times, is a cost-effective and reliable approach for the confirmatory diagnosis of MSUD.

Consistency in the Assessment of Dried Blood Spot Specimen Size and Quality in U.K. Newborn Screening Laboratories

In 2015, U.K. newborn screening (NBS) laboratory guidelines were introduced to standardize dried blood spot (DBS) specimen quality acceptance and specify a minimum acceptable DBS diameter of ≥7 mm. The UK 'acceptable' avoidable repeat rate (AVRR) is ≤2%. To assess inter-laboratory variability in specimen acceptance/rejection, two sets of colored scanned images (n = 40/set) of both good and poor-quality DBS specimens were distributed to all 16 U.K. NBS laboratories for evaluation as part of an external quality assurance (EQA) assessment. The mean (range) number of specimens rejected in the first EQA distribution was 7 (1-16) and in the second EQA distribution was 7 (0-16), demonstrating that adherence to the 2015 guidelines was highly variable. A new minimum standard for DBS size of ≥8 mm (to enable a minimum of six sub-punches from two DBS) was discussed. NBS laboratories undertook a prospective audit and demonstrated that using ≥8 mm as the minimum acceptable DBS diameter would increase the AVRR from 2.1% (range 0.55% to 5.5%) to 7.8% (range 0.55% to 22.7%). A significant inverse association between the number of specimens rejected in the DBS EQA distributions and the predicted AVVR (using ≥8 mm minimum standard) was observed (r = -0.734, p = 0.003). Before implementing more stringent standards, the impact of a standard operating procedure (SOP) designed to enable a standardized approach of visual assessment and using the existing ≥7 mm diameter (to enable a minimum of four sub-punches from two DBS) as the minimum standard was assessed in a retrospective audit. Implementation of the SOP and using the ≥7 mm DBS diameter would increase the AVRR from 2.3% (range 0.63% to 5.3%) to 6.5% (range 4.3% to 20.9%). The results demonstrate that there is inconsistency in applying the acceptance/rejection criteria, and that a low AVVR is not an indication of good-quality specimens being received into laboratories. Further work is underway to introduce and maintain standards without increasing the AVRR to unacceptable levels.

Satisfaction with home blood sampling methods and expectations for future point-of-care testing in phenylketonuria: Perspectives from patients and professionals

INTRODUCTION

Phenylketonuria (PKU) requires regular phenylalanine monitoring to ensure optimal outcome. However, home sampling methods used for monitoring suffer high pre-analytical variability, inter-laboratory variability and turn-around-times, highlighting the need for alternative methods of home sampling or monitoring.

METHODS

A survey was distributed through email and social media to (parents of) PKU patients and professionals working in inherited metabolic diseases in Denmark, The Netherlands, and United Kingdom regarding satisfaction with current home sampling methods and expectations for future point-of-care testing (POCT).

RESULTS

210 parents, 156 patients and 95 professionals completed the survey. Countries, and parents and patients were analysed together, in absence of significant group differences for most questions. Important results are: 1) Many patients take less home samples than advised. 2) The majority of (parents of) PKU patients are (somewhat) dissatisfied with their home sampling method, especially with turn-around-times (3-5 days). 3) 37% of professionals are dissatisfied with their home sampling method and 45% with the turn-around-times. 4) All responders are positive towards developments for POCT: 97% (n = 332) of (parents of) patients is willing to use a POC-device and 76% (n = 61) of professionals would recommend their patients to use a POC-device. 5) Concerns from all participants for future POC-devices are costs/reimbursements and accuracy, and to professionals specifically, accessibility to results, over-testing, patient anxiety, and patients adjusting their diet without consultation.

CONCLUSION

The PKU community is (somewhat) dissatisfied with current home sampling methods, highlighting the need for alternatives of Phe monitoring. POCT might be such an alternative and the community is eager for its arrival.

Use of dried blood spots for monitoring inflammatory and nutritional biomarkers in the elderly

OBJECTIVES

Blood microsampling, particularly dried blood spots (DBSs), is an attractive minimally-invasive approach that is well suited for home sampling and predictive medicine associated with longitudinal follow-up of the elderly. However, in vitro diagnostic quantification of biomarkers from DBS poses a major challenge. Clinical mass spectrometry can reliably quantify blood proteins in various research projects. Our goal here was to use mass spectrometry of DBS in a real-world clinical setting and compared it to the standard immunoassay method. We also sought to correlate DBS mass spectrometry measurements with clinical indices.

METHODS

A clinical trial of diagnostic equivalence was conducted to compare conventional venous samples quantified by immunoassay and DBSs quantified by mass spectrometry in an elderly population. We assayed three protein biomarkers of nutritional and inflammatory status: prealbumin (transthyretin), C-reactive protein, and transferrin.

RESULTS

The analysis of DBSs showed satisfactory variability and low detection limits. Statistical analysis confirmed that the two methods give comparable results at clinical levels of accuracy. In conclusion, we demonstrated, in a real-life setting, that DBSs can be used to measure prealbumin, CRP and transferrin, which are commonly used markers of nutritional status and inflammation in the elderly. However, there was no correlation with patient frailty for these proteins.

CONCLUSIONS

Early detection and regular monitoring of nutritional and inflammatory problems using DBS appear to be clinically feasible. This could help resolve major public health challenges in the elderly for whom frailty leads to serious risks of health complications.

A computer vision approach to the assessment of dried blood spot size and quality in newborn screening

BACKGROUND

Dried blood spot (DBS) size and quality affect newborn screening (NBS) test results. Visual assessment of DBS quality is subjective.

METHODS

We developed and validated a computer vision (CV) algorithm to measure DBS diameter and identify incorrectly applied blood in images from the Panthera DBS puncher. We used CV to assess historical trends in DBS quality and correlate DBS diameter to NBS analyte concentrations in 130,620 specimens.

RESULTS

CV estimates of DBS diameter were precise (percentage coefficient of variation <1.3%) and demonstrated excellent agreement with digital calipers with a mean (standard deviation) difference of 0.23mm (0.18mm). An optimised logistic regression model showed a sensitivity of 94.3% and specificity of 96.8% for detecting incorrectly applied blood. In a validation set of images (n=40), CV agreed with an expert panel in all acceptable specimens and identified all specimens rejected by the expert panel due to incorrect blood application or DBS diameter >14mm. CV identified a reduction in unsuitable NBS specimens from 25.5% in 2015 to 2% in 2021. Each mm decrease in DBS diameter decreased analyte concentrations by up to 4.3%.

CONCLUSIONS

CV can aid assessment of DBS size and quality to harmonize specimen rejection both within and between laboratories.

New Perspectives of Multiplex Mass Spectrometry Blood Protein Quantification on Microsamples in Biological Monitoring of Elderly Patients

Blood microsampling combined with large panels of clinically relevant tests are of major interest for the development of home sampling and predictive medicine. The aim of the study was to demonstrate the practicality and medical utility of microsamples quantification using mass spectrometry (MS) in a clinical setting by comparing two types of microsamples for multiplex MS protein detection. In a clinical trial based on elderly population, we compared 2 µL of plasma to dried blood spot (DBS) with a clinical quantitative multiplex MS approach. The analysis of the microsamples allowed the quantification of 62 proteins with satisfactory analytical performances. A total of 48 proteins were significantly correlated between microsampling plasma and DBS (p < 0.0001). The quantification of 62 blood proteins allowed us to stratify patients according to their pathophysiological status. Apolipoproteins D and E were the best biomarker link to IADL (instrumental activities of daily living) score in microsampling plasma as well as in DBS. It is, thus, possible to detect multiple blood proteins from micro-samples in compliance with clinical requirements and this allows, for example, to monitor the nutritional or inflammatory status of patients. The implementation of this type of analysis opens new perspectives in the field of diagnosis, monitoring and risk assessment for personalized medicine approaches.

Improved Dried Blood Spot PCR Assay for Universal Congenital Cytomegalovirus Screening in Newborns

Congenital cytomegalovirus (cCMV) is the most common perinatal infection, the leading cause of nongenetic sensorineural hearing loss, and one of the leading causes of neurodevelopmental impairment in the developed world. Early identification via newborn screening (NBS) would benefit the many undiagnosed infants who are either asymptomatic or mildly to moderately symptomatic, of whom 20% develop sequelae. The sensitivity of a recently developed PCR-based method to detect CMV in dried blood spots (DBS) is less than 80% and requires significantly more specimen than any other NBS test. We sought to improve the analytical sensitivity of the screening method by using droplet digital PCR and direct PCR and decreasing the amount of specimen utilized. The methods were tested with CMV-spiked filters, DBS from CMV-spiked cord blood, and DBS from neonates with cCMV. The results showed that the analytical sensitivity of all modified methods was equivalent to that of the reference method, with consistent CMV detection at high viral loads and inconsistent detection at low viral loads. IMPORTANCE Implementation of screening for cCMV in public health programs is hindered by feasibility challenges, including limited specimen availability and an insufficiently sensitive DBS-based screening assay. We report on efforts to improve the currently available DBS-based molecular assay to increase its feasibility of implementation in newborn screening programs. Although the analytical sensitivity of the modified methods was similar at the lower IU, equivalent CMV detection was achieved using one punch instead of the required three punches for the reference method. This reduction in sample size has the potential to substantially improve feasibility of NBS for cCMV. A population-based study is needed to further evaluate the clinical sensitivity of the improved assay.

Current State and Innovations in Newborn Screening: Continuing to Do Good and Avoid Harm

In 1963, Robert Guthrie's pioneering work developing a bacterial inhibition assay to measure phenylalanine in dried blood spots, provided the means for whole-population screening to detect phenylketonuria in the USA. In the following decades, NBS became firmly established as a part of public health in developed countries. Technological advances allowed for the addition of new disorders into routine programmes and thereby resulted in a paradigm shift. Today, technological advances in immunological methods, tandem mass spectrometry, PCR techniques, DNA sequencing for mutational variant analysis, ultra-high performance liquid chromatography (UPLC), iso-electric focusing, and digital microfluidics are employed in the NBS laboratory to detect more than 60 disorders. In this review, we will provide the current state of methodological advances that have been introduced into NBS. Particularly, 'second-tier' methods have significantly improved both the specificity and sensitivity of testing. We will also present how proteomic and metabolomic techniques can potentially improve screening strategies to reduce the number of false-positive results and improve the prediction of pathogenicity. Additionally, we discuss the application of complex, multiparameter statistical procedures that use large datasets and statistical algorithms to improve the predictive outcomes of tests. Future developments, utilizing genomic techniques, are also likely to play an increasingly important role, possibly combined with artificial intelligence (AI)-driven software. We will consider the balance required to harness the potential of these new advances whilst maintaining the benefits and reducing the risks for harm associated with all screening.

Screening method for the simultaneous determination of allantoin and uric acid from dried blood spots

Uric acid and its oxidation product allantoin are excellent biomarkers of oxidative stress in humans. Currently, there are high requirements not only for tests monitoring oxidative stress but also for screening laboratory tests in general. The highest demand is imposed on the simplest sampling, easy transport of the sample, and the shortest possible analysis time. The possible solution how to fulfil the requirements is sampling by dried blood spot technique with subsequent HPLC-MS/MS analysis. A fast, sensitive, and reliable HPLC-MS/MS method for the simultaneous determination of uric acid and allantoin from dried blood spots using stable isotopically labelled analogs as internal standards was developed. The separation took place in the reversed phase within 3 min, with protein precipitation and extraction in a one-step procedure. The analytical parameters of the method were satisfactory with an excellent linear range. The presented method was used to determine allantoin and uric acid levels in dried blood spot samples from 100 healthy volunteer donors. The median uric acid concentration in the cohort was 239.3 µmol/L and the median allantoin concentration was 5.6 µmol/L. The presented analytical protocol and method are suitable for screening and monitoring allantoin and uric acid levels as biomarkers of oxidative stress in clinical practice.

Automation of tacrolimus measurement on volumetric absorptive microsampling devices by tandem mass spectrometry

Aims: An automated method for the measurement of blood tacrolimus on volumetric absorptive microsampling (VAMS) devices was developed. Materials & methods: VAMS devices prepared by the automated method were compared with those prepared by the existing manual method (n = 284; mean concentration: 8.0 μg/l; range: 0.6-18.1). Results: The performance of both methods was comparable. Passing-Bablok regression demonstrated an acceptable correlation (y = -0.449 + 1.06x). Bland-Altman analysis demonstrated acceptable agreement (mean bias: -0.007 μg/l; standard deviation: 1.536). Automation reduced operator touch time by 40 min (48-sample batch). Conclusion: Automated preparation of VAMS devices reduced touch time and improved process consistency, facilitating high-throughput testing and transformation of existing laboratory workflows. Automation did not improve precision for VAMS devices but did so for liquid blood samples.

Effects of spot size on biomarker levels of field-collected dried blood spots: A new algorithm for exact dried blood spot size measurement

OBJECTIVES

The quality of blood values analyzed from survey-collected dried blood spot (DBS) samples is affected by fieldwork conditions, particularly spot size. We offer an image-based algorithm that accurately measures the area of field-collected DBS and we investigate the impact of spot size on the analyzed blood marker values.

METHODS

SHARE, a pan-European study, collected 24 000 DBS samples in 12 countries in its sixth wave. Our new algorithm uses photographs of the DBS samples to calculate the number of pixels of the blood-covered area to measure the spot sizes accurately. We ran regression models to examine the association of spot size and seven DBS analytes. We then compared the application of our new spot-size measures to common spot-size estimation.

RESULTS

Using automated spot-size measurement, we found that spot size has a significant effect on all markers. Smaller spots are associated with lower measured levels, except for HbA1c, for which we observe a negative effect. Our precisely measured spot sizes explain substantially more variance of DBS analytes compared to commonly used spot-size estimation.

CONCLUSION

The new algorithm accurately measures the size of field-collected DBS in an automated way. This methodology can be applied to surveys even with very large numbers of observations. The measured spot sizes improve the accuracy of conversion formulae that translate blood marker values derived from DBS into venous blood values. The significance of the spot-size effects on biomarkers in DBS should also incentivize the improvement of fieldwork training and monitoring.

Adult and neonate TSH blood spot reference intervals

BACKGROUND

Neonatal congenital hypothyroidism screening is performed by measuring thyroid-stimulating hormone (TSH) in a dried blood spot (DBS) sample, whereas acquired hypothyroidism uses serum TSH. There is no established DBS TSH reference interval, but knowing this is useful, as some patients cannot tolerate venepuncture, so DBS collection is seen as an acceptable alternative. The aim of this study was to establish DBS TSH reference intervals in adults and neonates (day 5-8), and determine the relationship between serum and DBS TSH.

METHODS

Euthyroid adults, not on thyroid medication and with a normal haematocrit, were selected. If they had a paired lithium heparin sample, DBS were prepared by spotting 50 µl of whole blood onto filter paper. DBS TSH was measured using the PerkinElmer Neonatal hTSH kit on the GSP instrument and serum using the Abbott Architect assay. The relationship between DBS and serum TSH was analysed using Passing-Bablok regression and the adult DBS TSH reference interval calculated using transformed data. The neonatal reference interval was calculated from screening results using the non-parametric method.

RESULTS

109 adult samples were included in the study (61 female). The Passing-Bablok regression was: DBS TSH = 0.68 x serum TSH + 0.07, and reference interval was 0.49-3.07 mU/L. The neonatal DBS reference interval was 0.40-4.10 mU/L from 8,351 results.

CONCLUSION

This study derived adult and neonate TSH DBS reference intervals using the GSP analyser and established the relationship between serum and DBS TSH. Knowing this information will allow for improved interpretation of DBS TSH results.

Parallel Reaction Monitoring Mode for Atenolol Quantification in Dried Plasma Spots by Liquid Chromatography Coupled with High-Resolution Mass Spectrometry

In this study, we reported a rapid, sensitive, robust, and validated method for atenolol quantification in dried plasma spots (DPS) by liquid chromatography with high-resolution mass spectrometry (LC-HRMS) using parallel reaction monitoring mode (PRM). Aliquots of 25 µL human plasma were placed onto Whatman 903 Cards and air-dried. Disks (3.2 mm internal diameter) were punched, and a 100 µL working internal standard solution was added to each sample and then incubated on a shaker for 15 min at 40 °C, followed by rapid centrifugation (10,000× g, 10 s). The supernatant was transferred into 300 µL vials for subsequent LC–HRMS analysis. After chromatographic separation, atenolol and the internal standard were quantified in positive-ion parallel reaction monitoring mode by detection of all target product ions at 10 ppm tolerances. The total time of the analysis was 5 min. The calibration curve was linear in the range of 5–1000 ng/mL with interday and intraday precision levels and biases of <14.4%, and recovery was 62.9–81.0%. The atenolol in DPS was stable for ≥30 days at 25 and 4 °C. This fully validated method is selective and suitable for atenolol quantitation in DPS using LC–HRMS.

Precise sample metering method by coordinated burst action of hydrophobic burst valves applied to dried blood spot collection

Dried blood spot (DBS) sampling by finger-pricking has recently gained a lot of interest as an alternative sample collection method. The reduced invasiveness, requirement of lower sample volumes and suitability for long-term storage at room temperature make DBS ideal for use in home settings or low-resource environments. However, traditional protocols often suffer from biased analysis data due to variable and not exactly known blood volumes present in the samples. In this work, a novel device has been developed to split-off precisely metered volumes from a blood drop and load them on pre-cut filter paper. Hereto, hydrophobic burst valves (HBV) were developed to temporarily retain a fluid flow, configurable to burst at pressures within a range of 175-600 Pa. By combining HBVs with different burst pressures, a volume metering system was developed to allow parallel metering of multiple pre-defined sample volumes. The system was shown to be accurate and consistent for blood volumes between 5-15 μL and for hematocrit levels spanning the range of 25-70%. Finally, a point-of-care DBS sampling device was developed combining the self-powered microfluidic SIMPLE technology. To evaluate the system's practical applicability, a validation study in the context of therapeutic drug monitoring of biologicals was performed using adalimumab-spiked blood samples. Microfluidic DBS samples showed good performance compared to the traditional DBS method with improved recovery rates (86% over 62%). This innovative metering system, allowing for parallelization and integration with complex liquid manipulations, will greatly impact the field of robust sampling, sample preparation, storage and analysis at the point-of-care.

[Main biological tools applied to newborn screening: Landscape and future perspectives]

Over the past fifty years, neonatal screening has become essential in the public health programs of a large number of countries. During all these years, the number of detectable diseases has continued to grow, following the possibilities offered by technical advances in clinical biology. The Guthrie test has enabled the miniaturization of blood sampling, opening up the possibilities of biological screening in the newborn population. Fluorimetry, immunoassay and more recently tandem mass spectrometry have subsequently allowed to detect many treatable disorders. The new developments of next generation sequencing and artificial intelligence may open a new era despite many ethical questions that will arise. This review provides an overview of the biological techniques currently used for neonatal screening and opens up perspectives on the place of new technological developments.

Use of Dried Blood Spot Specimens to Monitor Patients with Inherited Metabolic Disorders

Monitoring of patients with inherited metabolic disorders (IMDs) using dried blood spot (DBS) specimens has been routinely used since the inception of newborn screening (NBS) for phenylketonuria in the 1960s. The introduction of flow injection analysis tandem mass spectrometry (FIA-MS/MS) in the 1990s facilitated the expansion of NBS for IMDs. This has led to increased identification of patients who require biochemical monitoring. Monitoring of IMD patients using DBS specimens is widely favoured due to the convenience of collecting blood from a finger prick onto filter paper devices in the patient's home, which can then be mailed directly to the laboratory. Ideally, analytical methodologies with a short analysis time and high sample throughput are required to enable results to be communicated to patients in a timely manner, allowing prompt therapy adjustment. The development of ultra-performance liquid chromatography (UPLC-MS/MS), means that metabolic laboratories now have the capability to routinely analyse DBS specimens with superior specificity and sensitivity. This advancement in analytical technology has led to the development of numerous assays to detect analytes at low concentrations (pmol/L) in DBS specimens that can be used to monitor IMD patients. In this review, we discuss the pre-analytical, analytical and post-analytical variables that may affect the final test result obtained using DBS specimens used for monitoring of patients with an IMD.