Artificial elevation of phosphatidylethanol due to red blood cell transfusion.

Introduction: Phosphatidylethanol (PEth) is a marker of alcohol consumption used in clinical and forensic settings. PEth positivity in individuals expected to abstain from alcohol can have serious consequences. PEth is located on erythrocytes, thus packed red blood cell (pRBC) transfusion is a potential cause of false-positive results. This report is the first to demonstrate this phenomenon in an authentic patient who was negative for PEth immediately prior to transfusion.

Methods: Residual blood samples collected for clinical testing before and after pRBC transfusion and citrated pRBC segments were tested for PEth homologues 16:0/18:1 (POPEth) and 16:0/18:2 (PLPEth) by liquid chromatography - tandem mass spectrometry with limit of quantitation 10 ng/mL (0.01 µmol/L).

Case: A 56-year-old male with new-onset leukemia required transfusion of 4 pRBC units on hospital days 1-2. Blood collected at admission (day 0) showed POPEth and PLPEth < 10 ng/mL (<0.01 µmol/L). Blood collected after completion of the fourth pRBC transfusion demonstrated POPEth = 57 ng/mL (0.08 µmol/L), PLPEth = 38 ng/mL (0.05 µmol/L). One citrated segment demonstrated extremely elevated PEth, supporting pRBC transfusion as the source.

Discussion: This case demonstrates pRBC transfusion elevating PEth to concentrations associated with moderate alcohol consumption. Studies suggest that healthy individuals (potential donors) could have PEth concentrations sufficient to cause significant elevation of PEth from a single pRBC unit. This is concerning for populations such as liver transplant candidates who are required to abstain from alcohol, but whose disease sequelae may require pRBC transfusion.

Conclusions: pRBC transfusion can artificially elevate PEth into clinically and forensically relevant ranges. Individuals interpreting toxicology testing should consider recent pRBC transfusion when evaluating PEth concentrations.