Cutoff-dependent test responses and age, sex and seasonal variations of the alcohol biomarkers phosphatidylethanol (PEth) and carbohydrate-deficient transferrin (CDT)

< 0.0001) but with substantial individual variability. Clinical classification was concordant in most cases, 66% being negative for both and 16% being positive for both at routine cutoffs (PEth >0.30 µmol/L; CDT ≥2.0%). However, PEth alone was positive in 15% and CDT alone in ∼3%. PEth identified 90% of all positive cases (i.e. by PEth and/or CDT) compared with 57% for CDT, while 47% were positive for both. Increasing the PEth cutoff to >0.50 µmol/L reduced positivity to 66%, whereas lowering the CDT cutoff to ≥1.7% increased positivity to 90%. The prevalence of positive test results increased with age. For CDT, men showed higher positivity across all age groups, while PEth scored higher for men only in those aged 64,000 test per biomarker), the monthly average and proportion of positive PEth values correlated with population-level alcohol consumption showing peaks during summer holidays and after Christmas-New Year, whereas no correlation was observed for CDT. In conclusion, differences between PEth and CDT are largely driven by cutoff-dependent classification rather than discordant biomarker behavior.