Background: The past decades have witnessed a growing interest in patient-centric sampling, including capillary blood microsampling. Despite its advancements, a key issue lies in interpreting capillary blood results against existing plasma-based reference ranges. To address this challenge, various methodologies to convert capillary blood concentrations to plasma equivalents have been proposed.

Aims: This study aimed at systematically evaluating and comparing different methodologies for converting capillary blood-based to venous plasma-based results using clinical pharmacokinetic (PK) data of paracetamol and metabolites.

Methods: Paired finger-prick volumetric absorptive microsampling (VAMS) and venous blood samples were collected from 55 patients. For each analyte, VAMS-based results were converted using multiple approaches, including conversion based on the hematocrit (Hct), the median (time-dependent) capillary-to-plasma ratio, Passing-Bablok regression analysis, and linear mixed-effects modeling. Performance was assessed by comparing the agreement between converted capillary blood-based and actual plasma-based results to predefined analytical and clinical acceptance criteria.

Results: All approaches, except Hct-based conversion, yielded acceptable results, with minor variations in analytical performance. Additionally, the time after paracetamol dosing proved to be a significant covariate for adequate conversion for all except one analytes. Predicted Cmax and AUC0-t values using converted VAMS-based results were within bio-equivalence criteria (80–125%) for all, but one (i.e., Hct), conversion approaches.

Conclusions: Both from analytical and clinical perspectives, this study demonstrated the reliability of different approaches to convert capillary blood-based to plasma-based results. Additionally, this study framework may guide future microsampling-based studies aiming at converting capillary blood concentrations.

Key Words: Microsampling, Conversion Approaches, VAMS, Pharmacokinetics

Background:
Over 80% of the rate-limiting step in 5-fluorouracil degradation is catalysed by the pivotal DPD enzyme. Known risk factors for severe toxicity are (partial) DPD deficiencies, which are currently evaluated prior to chemotherapy by DPD phenotyping. The latter encompasses determination of the endogenous analytes uracil and dihydrouracil, with elevated plasma uracil indicating impaired DPD functionality, requiring treatment adjustment. However, challenges arise in the preanalytical phase, as uracil levels quickly rise after blood sampling, risking false positive results.

Aims:
Assess whether dried blood spots (DBS) offer improved preanalytical stability in uracil determination.

Methods:
An LC-MS/MS method, targeting uracil, dihydrouracil and uridine, was developed to analyse (dried) blood samples. Stability in venous DBS was assessed after one week storage at ambient conditions and compared with liquid microsamples. A study in healthy volunteers was performed to evaluate differences between venous and capillary DBS.

Results:
Analyte concentrations in liquid whole blood exceeded the 15% threshold within 5h, with uracil rising to 700% after 48h. In venous DBS, uracil levels only slightly increased upon drying, stabilizing at a mean increase of 36%±17 for at least one week. Uracil concentrations were significantly higher in capillary than in venous DBS (264%±42) and showed large within-subject variation (26%). Variability in venous DBS remained limited.

Conclusion:
Capillary DBS showed both higher and inconsistent uracil levels compared to venous DBS. However, as preanalytical stability is significantly improved, with limited variation, this study suggests that venous DBS are possibly suitable for DPD phenotyping.

Key Words:
Microsampling, uracil, DPD, phenotyping, stability

Background: Healthcare accounts for 4-5% of the world’s carbon footprint. The carbon emissions associated with blood tests are predominantly generated through the transportation of the patient to a collection centre, the equipment used for sample collection and the transport of the sample to the laboratory. Transportation emissions are significant in countries like Australia where patients live in remote areas which are long distances from laboratories.

Aims: To calculate the carbon emissions from transportation of a Telimmune® card and frozen plasma sample from collection site to the laboratory (888km) and the total carbon savings in a pilot study.

Methods: The transportation carbon emissions were calculated using the Carboncare CO₂ Emissions Calculator (based on ISO 14083:2023) and the total carbon savings was based on 50 patients.

Results: The carbon emissions of transporting a frozen plasma sample and a Telimmune® Card were 2.56 and 0.01 kg Co₂e, respectively. The transport of the card produced 99.6% less carbon compared to plasma, a total savings of 127.4 kg of Co₂e.

Discussion: The use of microsampling devices for Therapeutic Drug Monitoring can reduce the carbon footprint of blood sampling with transport alone. A comprehensive Life Cycle Assessment of blood collection to include patient travel, sample collection, sample transport, sample packaging and storage conditions (before, after and during transport), and other microsampling devices is required to have a full understanding of the carbon savings of microsampling compared to traditional blood collection methods.

Keywords: Microsampling, Carbon Emissions, Sustainability in Healthcare, Environmental Impact, Blood Sample Transport, Therapeutic Drug Monitoring

Background: Epilepsy is a chronic neurologic disorder that significantly impacts on the everyday quality of life of patients. The use of multiple concomitant medications is associated to drug-drug interactions (DDIs) and highlights the utility of therapeutic drug monitoring (TDM). Volumetric absorptive microsampling (VAMS) are emerging tools for TDM of several drugs including antiepileptics (AEs).
Aim: To compare the concentrations of carbamazepine (CBZ), levetiracetam (LEV), lacosamide (LCS), topiramate (TPR) in both plasma and VAMS samples.
Methods: VAMS were collected by fingerprick in pediatric patients followed at our Centre. Patients were also subjected to conventional venous blood sampling. Plasma and VAMS samples were analysed by UHPLC-MS/MS using a validated kit for determination of AE (ClinMass LC-MS/MS Complete Kit®, RECIPE+). A cross-validation analysis was performed by using Spearman correlation coefficient (r), Deming regression and Bland-Altman plot.
Results: A positive significant correlation (p<0.001) was found between VAMS and plasma concentrations for CBZ (r=0.80) with its metabolites Diol (r=0.92) and Epoxide (r=0.90), LEV (r=0.87), LCS (r=0.91) and TPR (r=0.95). Bland-Altman analysis showed a % bias of -0.90 for CBZ, 7.76 for Diol, -0.55 for Epoxide, 4.56 for LEV, -13.09 for TPR and -12.22 for LCS.
Conclusions: Our results show a good agreement between plasma and VAMS, suggesting their use for TDM of AEs during the routine clinical practice. Due to the low blood volume required, VAMS are a compliant alternative to conventional venipuncture for pediatric patients, and, following an adequate cross-validation, they could represent a valid opportunity for promoting remote TDM.

Background: Steroid hormone measurement in blood is crucial for diagnosing and monitoring endocrine disorders, including congenital adrenal hyperplasia (CAH), which results from enzymatic defects in the steroidogenesis pathway. CAH patients require lifelong hormone replacement therapy to manage adrenal insufficiency and regulate excess androgen levels. Microsampling provides a less invasive alternative to frequent venous blood sampling, particularly in paediatric CAH patients, enabling at-home follow-up.

Aims: The aim of this study was to set up a microsampling method utilizing 20 µL VAMS samples for determining androstenedione, 17α-hydroxyprogesterone and 11-ketotestosterone to follow-up CAH patients.

Methods: LC-MS/MS methods were developed and optimized for a broad panel of endogenous steroids, including testosterone, androstenedione, 17α-hydroxyprogesterone and 11-ketotestosterone, allowing broad applicability of the method. An extraction protocol for VAMS samples was optimized to maximize the sensitivity of the method and samples from healthy volunteers were analysed.

Results: Two separate LC-MS/MS methods were developed, allowing detection in either positive or negative ionization mode and allowing separation of all isomeric compounds. A liquid-liquid extraction protocol was optimized resulting in an LLOQ as low as 20 pg/mL for androstenedione and 500 pg/mL for 17α-hydroxyprogesterone. Endogenous levels of androstenedione and 17α-hydroxyprogesterone could be measured in 20 µL VAMS samples from healthy volunteers.

Conclusions: A sensitive LC-MS/MS method was developed to determine a broad panel of endogenous steroids in 20 µL VAMS samples. Endogenous levels in healthy volunteers could be determined, confirming adequate sensitivity for use in CAH patients.

Key Words: Volumetric Absorptive Microsampling, Steroid profiling, Congenital Adrenal Hyperplasia

Background: Various DBS-based methods, both volumetric and non-volumetric, have been published for imatinib quantification, each proposing a unique correction factor (CF). Since CF represents the plasma-to-whole blood concentration ratio (or vice versa), it should ideally remain consistent across different assays.

Aims: This study aims to determine whether different DBS-methods for imatinib quantification yield the same CF, enabling cross-validation of conversion strategies across methods and patient samples, addressing the common challenge of limited sample size in clinical validation.

Methods: A DBS-based LC-MS method quantified imatinib in patient samples (NCT06822959) using Capitainer B and HemaXis DB10. Plasma concentrations were estimated using a blood-to-plasma CF. Statistical analyses included Passing–Bablok and Bland–Altman tests, with CF comparisons to previously published DBS-methods.

Results: An haematocrit independent (22-55%) LC-MS method for imatinib quantification in Capitainer B and HemaXis DB10 was developed and validated. Seventy five paired DBS and plasma samples were collected from 28 patients and used to calculate the CF (0.78 for Capitainer, 0.82 for HemaXis). A strong correlation (percentage difference within ±20% in > 90%) between the estimated and actual plasma concentrations for both devices was observed and statistically demonstrated. The same agreement (> 90%) was observed when using the CFs previously proposed in different DBS-methods (2 non-volumetric assays and 1 using VAMS).

Conclusions: All the calculated CFs accurately represent the relationship between plasma and DBS concentrations across various DBS-based methods, making them applicable to future methods regardless of characteristics such as volumetric/non-volumetric DBS or collection device type.

Keywords: imatinib, TDM, DBS, LC-MS

Background: Microsampling is an alternative sampling strategy for adherence monitoring. Some devices like volumetric absorptive microsampling (VAMS) and Capitainer-B allow the collection of defined volumes of capillary blood. Both have already been successfully applied for therapeutic drug monitoring and adherence assessment.

Aims: The aim was to develop a microsampling procedure to be used for adherence monitoring of 15 drugs in the context of coronary artery disease (CAD). Sampling by VAMS and Capitainer-B should be evaluated and compared.

Methods: Amlodipine, atenolol, atorvastatin, bisoprolol, carvedilol, clopidogrel, diltiazem, lercanidipine, metoprolol, nebivolol, prasugrel, rosuvastatin, salicylic acid, simvastatin hydroxy acid, and verapamil were included. VAMS-tips and Capitainer-B-disks loaded with 10 µL capillary blood were extracted by adding 200 µL of methanol. After shaking and centrifugation, the supernatant was evaporated, reconstituted, and analyzed using an LC-Orbitrap system. Isotope dilution mass spectrometry was used for quantification and the validation was based on recommendations of e.g., the European Medicines Agency and the IATDMCT.

Results: Both devices were found to be suitable for sample collection and extraction. Selectivity was given for all analytes except for prasugrel. Matrix effects for Capitainer-B were higher for most analytes compared to VAMS. Isotope dilution mass spectrometry allowed the quantification of all analytes except prasugrel. Accuracy and precision data were acceptable with exception of lercanidipine (both devices) and atorvastatin (only Capitainer-B).

Conclusions: A quantitative method for analysis of 15 drugs used for the treatment of CAD was successfully developed and validated, and shall be applied for future adherence monitoring.

Keywords: Microsampling, LC-MS, Adherence, Validation