A validated method for capillary phosphatidylethanol 16:0/18:1 quantification with two different 10-µl volumetric absorptive microsample devices in the same setup.

There is a growing interest for quantification of drugs in capillary blood. Phosphatidylethanol (PEth) is a biomarker for alcohol intake measured in whole blood, thus making it a candidate for capillary sampling. Our laboratory has been running a method for PEth quantification in venous blood since 2016, and we aimed to expand this method to also include capillary dried blood spot (DBS) samples. Two 10-µl volumetric absorptive microsampling (VAMS) devices, Capitainer®B Vanadate and Mitra®, were included in the method development and validated. Calibrators and quality controls were spiked during automatic sample extraction without the VAMS devices present, making it possible to extract and analyze both types of VAMS samples in the same setup. With the Mitra device, all pre-established validation criteria were fulfilled in the measuring range of 0.03 to 4.0 µM (21-2812 ng/mL), including method comparison with our venous blood method. Capitainer fulfilled all validation criteria, except for the accuracy of samples with PEth levels ≥ 0.5 µM (≥ 352 ng/mL) (deviation -17.1% to -20.5%). The correlation analysis between Capitainer and the venous blood results showed no constant bias, but an acceptable small proportional mean difference of -7.6%. Overall, the method validation results for both Capitainer and Mitra were considered acceptable. Both devices were found to be suitable for the analyses of PEth.