Results

Overall cohort

Excluding 13 samples due to paired consecutive blood samples in drinking-after-driving cases, the study included 87 individuals, with 77 males and 10 females. The mean age of the subjects was 37 years (median: 33 years, range: 17–74 years).

BAC analysis revealed that 64 individuals (73.5%) had a BAC ≥ 1.1 g/kg, corresponding to the legal threshold for absolute driving incapacity in Germany. Among them, 41 exhibited BACs ≥ 1.6 g/kg (47.1%), while 10 individuals had a BAC below 0.5 g/kg and three individuals tested negative for alcohol (Fig. 1).

Fig. 1: Absolute frequencies of grouped blood alcohol concentrations (BACs) in g/kg for the overall cohort and the driving-under-influence (DUI) cohort

The median blood concentration of EtG was 2,975 ng/mL (range: above cutoff of 1 ng/mL to 8,627 ng/mL, mean: 2,911 ng/ml), with 96.6% of cases exceeding 100 ng/ml. PEth 16:0/18:1 concentrations showed a median of 140 ng/mL, ranging from LLOQ (9.1 ng/ml) to 1,520 ng/mL (mean: 252 ng/ml). In total, 35 individuals (40.2%) exhibited PEth concentrations ≥ 200 ng/ml and 3 cases were below 20 ng/ml.

Of the three individuals with negative BAC results, two also had EtG and PEth concentrations below the respective detection limits. The third individual, despite a negative BAC, showed a PEth concentration of 99.4 ng/mL and an EtG concentration of 35.6 ng/mL.

None of the individuals with BACs below 0.5 g/kg had PEth concentrations ≥ 200 ng/mL, whereas 31 of 64 (48%) individuals with BACs ≥ 1.1 g/kg did. Among the 41 individuals with BAC ≥ 1.6 g/kg, there were 25 (61%) individuals with PEth concentrations above 200 ng/ml, but still five (12%) with PEth values below 100 ng/ml, see also Fig. 2.

Fig. 2: Absolute and relative distribution of PEth groups by BAC groups in the overall cohort (n = 87)

A strong positive correlation was observed between BAC and EtG concentrations in blood (r = 0.778, p < 0.01), confirming the close relationship between acute alcohol intake and EtG concentrations (Fig. 3). In contrast, BAC and PEth concentrations showed a moderate correlation (r = 0.497, p < 0.01) (see Fig. 4), suggesting that although PEth concentrations increase with BAC, individual variability in drinking patterns likely modulates the strength of this relationship.

Fig. 3: Scatterplot of BAC (g/kg) and EtG (ng/mL), with DUI cases highlighted in red

Fig. 4: Scatterplot of BAC (g/kg) and PEth (ng/ml), with DUI cases highlighted in red

To evaluate PEth not only as a marker of chronic alcohol use but also as a potential indicator of recent or acute consumption, EtG and BAC were analyzed across incremental PEth categories (< 100 ng/mL, 100–199 ng/mL, ≥ 200 ng/mL), as shown in Figs. 5 and 6.

Fig. 5: Distribution of EtG concentrations by PEth groups: left panel shows the overall sample (n = 87), right panel shows DUI cases (n = 76)

Fig. 6: Distributions of BACs by PEth groups: left panel shows teh overall sample (n = 87), right panel shows DUI cases (n = 76)

In the PEth < 100 ng/mL group, the median EtG concentration was 1,647 ng/mL (mean ± SD: 1,716 ± 1,121 ng/ml), and the median BAC was 1.04 g/kg (mean ± SD: 1.03 ± 0.6). Concentrations were more heterogeneous in this group, with EtG ranging from below the cutoff to 3,998 ng/mL and BAC from 0 to 2.11 g/kg, indicating substantial variability in recent drinking behavior.

In the PEth 100 – <200 ng/mL group, median EtG increased to 2,975 ng/mL (mean ± SD: 2,803 ± 1,381 ng/ml), and the median BAC to 1.56 g/kg (mean ± SD: 1.63 ± 0.63 g/kg). Maximum concentrations reached 5,422 ng/mL for EtG and 2.65 g/kg for BAC, with two BAC outliers (0.18 and 0.3 g/kg) observed.

In the PEth ≥ 200 ng/mL group, both markers reached their highest concentrations, with a median EtG of 3,789 ng/mL (mean ± SD: 3,972 ± 1,623 ng/ml) and a median BAC of 1.93 g/kg (mean ± SD: 1.94 ± 0.56 g/kg). Maximum concentrations were 8,627 ng/mL for EtG and 2.95 g/kg for BAC.

DUI-cases

Of the 87 individuals, 76 were involved in DUI incidents, while the remaining 11 were suspected of non-traffic-related offenses. Among DUI cases, the majority operated cars (n = 54), followed by bicycles/e-bikes (n = 11), e-scooters (n = 6), mopeds (n = 3), and motorcycles (n = 2).

Within the DUI group, 73.7% of individuals (n = 56) exceeded the legal threshold for absolute driving incapacity in Germany (BAC ≥ 1.1 g/kg), and 46.1% (n = 35) exhibited BACs ≥ 1.6 g/kg Conversely, 9.2% (n = 7) had BACs below the administrative offence limit of 0.5 g/kg, including three individuals with BACs < 0.3 g/kg (see Fig. 1).

The median EtG concentration among DUI cases was 2,608 ng/mL (range: below cutoff – 8,627 ng/mL). The median PEth concentration was 125 ng/mL (range: below cutoff − 1,520 ng/mL), with 36.8% of individuals (n = 28) showing PEth ≥ 200 ng/ml.

Of the 35 individuals within the DUI group with BACs ≥ 1.6 g/kg — and thus required to undergo an assessment of fitness to drive — 54.3% showed PEth concentrations ≥ 200 ng/mL, indicating drinking patterns inconsistent with a single episode of excessive alcohol intake. Only five (14.3%) in this group showed PEth concentrations < 100 ng/ml. The median EtG concentration in this group was 3,720 ng/mL (range: 780–8,627 ng/mL).

Correlations among BAC, EtG and PEth in the DUI subgroup were consistent with those in the overall cohort showing a strong positive correlation between BAC and EtG (r = 0.767), and moderate correlations between BAC and PEth (r = 0.502) as well as EtG and PEth (r = 0.556).