Abstract
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.
Highlights
Therapeutic drug monitoring (TDM) of immunosuppressant drugs has been part of routine transplant patient care for decades
The limit of clinical acceptance was set a priori at 85%–115% around the ratio of matched whole blood (WB)-dried blood spot (DBS) and matched WB-volumetric absorptive microsampling (VAMS) samples for at least 80% of the samples in accordance with earlier studies [13, 27]. These limits were chosen in a multidisciplinary team consisting of transplantation nephrologists, pharmacists and analysts and were based on current trough concentration targets and the relevant concentration window for tacrolimus in kidney transplantation in combination with the aspects of the analytical method used for VAMS, DBS and WB [1, 13, 32,33,34,35]
The imprecision is the variance of the predicted values which is measured by the root median squared prediction error (RMSE) and the median absolute percentage prediction error (MAPE)
Summary
Therapeutic drug monitoring (TDM) of immunosuppressant drugs has been part of routine transplant patient care for decades. Because of great inter- and intra-individual variation in pharmacokinetics (PK), dosing of these drugs is tailored for each patient based on the blood drug concentration This results in frequent patient visits to the hospital for venous blood sampling. The sample can be sent to the laboratory by mail This decreases patient burden and allows more flexible immunosuppressant monitoring [8, 12]. Several of these DBS methods have shown to yield interchangeable results with venous whole blood (WB) and are routinely applied in transplant patient care, including in our hospital [2, 3, 11, 13]. A drawback of DBS application is that sampling by the patient does not always lead
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