Discussion

This study investigated the relationship between BAC, EtG, and PEth with a focus on traffic offenders. The results demonstrate a consistent association between acute alcohol intoxication, recent drinking behavior, and long-term alcohol use, as measured by BAC, EtG, and PEth, respectively.

A strong positive correlation between BAC and EtG (r = 0.778, p < 0.01) confirms EtG as a reliable biomarker for recent alcohol intake, typically within the past few hours [3]. The gradual increase in EtG concentrations across increasing PEth categories holds limited significance during acute intoxication, as the duration of intoxication among the subjects is unknown and EtG levels continue to rise with ongoing alcohol metabolism. Nevertheless, these patterns support the use of EtG and PEth as complementary biomarkers for assessing different temporal dimensions of alcohol intake — a concept further substantiated by Neumann et al., who demonstrated that the combined measurement of PEth, EtG, and ethanol in blood provides a more robust characterization of drinking behavior in both clinical and forensic settings [11].

PEth concentrations showed a moderate correlation with BAC (r = 0.497, p < 0.01), and median BAC increased from 1.04 g/kg in individuals with low PEth levels to 1.93 g/kg in those with PEth ≥ 200 ng/mL. This may reflect that individuals with evidence of habitual drinking also tend to present with higher concentrations of acute intoxication. However, overlapping BACs within PEth categories underscore the influence of individual factors such as tolerance, drinking pattern, and timing of last consumption. Supporting these findings, Schröck et al. demonstrated that PEth analysis in blood can help distinguish between social drinking and excessive alcohol use in DUI cases [9]. Similarly, Dağlıoğlu et al. reported a strong positive correlation between PEth and BAC (r = 0.784) in traffic accident cases, highlighting the utility of PEth — particularly in combination with EtG — for the forensic evaluation of alcohol consumption [12].

Studies showed that even low to moderate drinking events in previously abstinent individuals can yield PEth concentrations above 20 ng/mL [13, 14]. Similarly, Spleis et al. demonstrated that consumption of 0.6–0.75 g/kg ethanol can result in PEth concentrations above common forensic thresholds, depending on drinking context and metabolism [15]. These findings underline the importance of interpreting PEth concentrations carefully, especially when considering abstinence verification or differentiating one-time from repeated use.

In Germany, suspects of DUI are required to provide a blood sample if breath alcohol testing is refused, not feasible or if individuals are suspected of having committed an alcohol related criminal offense. In such cases the combined analysis of BAC, EtG, and PEth provides greater diagnostic depth than any single marker alone. While BAC reflects only acute intoxication and does not account for drinking patterns, this becomes particularly relevant when high BACs are observed without corresponding clinical signs of intoxication, suggesting alcohol tolerance or chronic consumption. The inclusion of PEth and EtG allows experts to evaluate whether a high BAC is the result of on-time intake or habitual drinking— an essential distinction in both criminal liability and driver`s licensing assessments.

In Germany, PEth concentrations ≥ 20 ng/mL are considered indicative of recent drinking, while concentrations ≥ 200 ng/mL in clinical context [6] resp. ≥210 ng/mL in forensic cases [8] suggest chronic use. EtG concentrations > 5 ng/mL in blood are widely accepted as indication of recent alcohol consumption. Most individuals in this study exceeded one or both thresholds, indicating substantial alcohol use among traffic offenders and supporting the integration of PEth and EtG testing into routine forensic assessments.

In 2023, about 657,000 verdicts were issued by German criminal courts, with roughly 17% related to traffic offenses (e.g., § 316 German criminal code) [16]. Bavarian data show that around 43% of traffic offences involved alcohol [17]. In our study, 48% of individuals with BACs ≥ 1.1 g/kg had PEth concentrations above 200 ng/mL, indicating habitual rather than isolated drinking. Extrapolated nationally, approximately 23,000 court evaluations could benefit from combined EtG and PEth testing.