Assessment and cross-validation of calibration transferability between dried blood spot sampling devices for accurate quantification of phosphatidylethanol.

Phosphatidylethanol (PEth) is a direct alcohol biomarker which is used in a variety of clinical and forensic contexts. Due to its limited stability in whole blood, PEth is routinely analysed using dried blood spots (DBS). There are many different commercially available sampling systems for DBS, but data on their comparability is scarce. The aim of this study was to develop and validate a LC-MS/MS method for the quantification of PEth 16:0/18:1 and PEth 16:0/18:2 for three different DBS sampling systems: Whatman™ filter paper (903 Protein Saver Cards), Mitra and CapitainerB Vanadate. The transferability of calibration curves and their applicability across these devices should be assessed. The results showed that DBS of all devices could be prepared and analysed using the same procedure. Validation was successful for the devices. The accuracy of QCs was best if quantified using the matching DBS sampling device calibration curve (bias < 15 %). Higher, but still acceptable, bias values were observed when using a Whatman™ calibration curve to quantify PEth in DBS of the CapitainerB Vanadate system and vice versa. Mitra QCs should only be quantified using device-specific calibration curves, as in all other cases, accuracy exceeded the limit of 15 %. We recommend analysing samples using device-specific calibrations at all times, as determined PEth concentrations might be crucial for patients and should not be subjected to any avoidable uncertainty.