Limited added utility of urine ethyl glucuronide compared to blood phosphatidylethanol in a predominantly transplant population.

Background: Alcohol biomarkers including ethyl glucuronide (EtG) and phosphatidylethanol (PEth) are ordered frequently in clinical and forensic settings including solid organ transplantation. PEth provides a long detection window but can be insensitive to light drinking. In contrast, EtG and ethyl sulfate (EtS) can be elevated after light alcohol consumption and might complement PEth testing.

Methods: Urine EtG/EtS and whole blood PEth results were evaluated from all clinically-ordered testing between 2014-2024. PEth and EtG/EtS confirmation were performed by liquid chromatography tandem mass spectrometry at two reference laboratories, using cutoffs: Lab A, PEth 20 ng/mL, EtG and EtS 500 and 250 ng/mL; Lab B, PEth 10 ng/mL, EtG and EtS 250 and 100 ng/mL. Only Lab B performed EtG screening by immunoassay, using a 500 ng/mL cutoff.

Results: PEth was positive in 1269 (15.6%) of 8131 samples, compared to 769 (6.7%) confirmed EtG/EtS positives from 11555 samples. EtG screening (n = 9668) was positive in 743 (7.7%) samples, of which 30 (4.0%) confirmed negative (false positives); the screen was indeterminate in 267 (2.8%) samples, 66 of which confirmed positive and 172 negative. Of 3132 paired PEth and EtG samples, 2887 (92.2%) were concordant, 224 (7.2%) were PEth-positive and 21 (0.7%) were EtG-positive. PEth was significantly more sensitive in paired samples (p < 0.001), even after accounting for potential confounders. Limiting testing to PEth would have correctly identified alcohol consumption in 331 of 373 (88.7%) instances versus EtG/EtS in 149 (39.9%), and reduced charges by >$720,000 USD.

Discussion: PEth outperformed EtG/EtS in detecting alcohol consumption in a predominantly abstinent transplant population. Compared to PEth, EtG/EtS had lower overall positivity and poorer sensitivity in paired samples; additionally, EtG screening demonstrated false positives and indeterminate results. EtG testing provided little added value beyond PEth in this population, and did not warrant the increased cost of performing both tests.