Patient-centric capillary dried blood spot sampling for tacrolimus and creatinine monitoring in clinical practice

Abstract Objectives Therapeutic drug monitoring (TDM) of tacrolimus is essential due to its high inter- and intra-patient variability and narrow therapeutic window. Conventional venous blood sampling may limit sampling frequency and patient convenience. Capillary dried blood spot (DBS) sampling represents a patient-centric alternative that could enable decentralized monitoring and longitudinal follow-up in clinical practice. Methods The aim of this study was to evaluate the clinical applicability of capillary finger prick sampling for tacrolimus TDM and creatinine determination in the hospital (part 1), and at home (part 2), using conventional DBS and Capitainer ® qDBS devices. Previously validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis methods were used. Additionally, sample quality and patient experience were assessed. Results The assisted sampling part of the study revealed the clinical applicability of conventional DBS and Capitainer ® qDBS sampling as a complementary tool for tacrolimus TDM and creatinine determination after capillary finger prick, with Capitainer ® qDBS showing better clinical agreement (93 % of tacrolimus and 87 % of creatinine results within 15 % of the mean). Home sampling using Capitainer ® qDBS devices was found to be feasible in allo-SCT patients, who also positively scored the user-friendliness of the device. Conclusions Capillary qDBS show great potential as a complement to venous blood draws for tacrolimus and creatinine determination in TDM workflows. Integration of home-based sampling allows better longitudinal assessment of drug exposure and renal function, providing laboratory insight into intra-patient variability and adherence, contributing to more informed, individualized TDM.