Clinical validation of two volumetric absorptive microsampling devices to support home‐based therapeutic drug monitoring of immunosuppression

Abstract

AimsDried blood volumetric absorptive microsamples (VAMS) may facilitate home‐based sampling to enhance therapeutic drug monitoring after transplantation. This study aimed to clinically validate a liquid chromatography–tandem mass spectrometry assay using 2 VAMS devices with different sampling locations (Tasso‐M20 for the upper arm and Mitra for the finger). Patient preferences were also evaluated.MethodsClinical validation was performed for tacrolimus and mycophenolic acid by comparison of paired VAMS and venipuncture samples using Passing–Bablok regression and Bland–Altman analysis. Conversion of mycophenolic acid VAMS to serum concentrations was evaluated using haematocrit‐dependent formulas and fixed correction factors defined a priori. Patients' perspectives, including useability, acceptability and feasibility, were also investigated using established questionnaires.ResultsPaired samples (n = 50) were collected from 25 kidney transplant recipients. Differences for tacrolimus whole‐blood concentration were within ±20% for 86 and 88% of samples from the upper arm and fingerstick, respectively. Using correction factors of 1.3 for the upper‐arm and 1.47 for finger‐prick samples, 84 and 76% of the paired samples, respectively, were within ±20% for mycophenolic acid serum concentration. Patient experience surveys demonstrated limited pain and acceptable useability of the upper‐arm device.ConclusionsTacrolimus and mycophenolic acid can be measured using 2 common VAMS devices with similar analytical performance. Patients are supportive of home‐based monitoring with a preference for the Tasso‐M20 device.