Clinical performance of volumetric finger-prick sampling for the monitoring of tacrolimus, creatinine and haemoglobin in kidney transplant recipients.

Aims: Finger-prick sampling has emerged as an attractive tool for therapeutic drug monitoring and associated diagnostics. We aimed to validate the clinical performance of using two volumetric devices (Capitainer® qDBS and Mitra®) for monitoring tacrolimus, creatinine and haemoglobin in kidney transplant (KTx) recipients. Secondarily, we evaluated potential differences between finger-prick sampling performed by healthcare professionals vs. self-sampling, and differences between the two devices.

Methods: We compared finger-prick and venous sampling in three settings: microsampling performed by healthcare personnel, self-sampling under supervision, unsupervised self-sampling. The finger-prick samples were analysed with adapted methods and results compared to routine method analysis of the venous blood samples.

Results: Twenty-five KTx recipients completed the main study and 12 KTx recipients completed a post hoc validation study. For tacrolimus measurements and predicted area under the curve, the proportions within ±20% difference were 79%-96% for Capitainer and 77%-95% for Mitra. For creatinine and haemoglobin, the proportions within ±15% were 92%-100% and 93%-100% for Capitainer and 79%-96% and 67%-92% for Mitra, respectively. Comparing sampling situations, the success rate was consistent for Capitainer (92%-96%), whereas Mitra showed 72%-88% and 52%-72% success rates with samples collected by healthcare personnel and the patients themselves.

Conclusions: Capitainer and Mitra are technically feasible for measuring tacrolimus, creatinine and haemoglobin. In the context of self-sampling, Capitainer maintained consistent sampling success and analytical quality. Implementing volumetric finger-prick self-sampling for the monitoring of tacrolimus, creatinine and haemoglobin may simplify and improve the follow-up of KTx recipients.