Introduction

The objective assessment of alcohol consumption patterns is essential in traffic medicine, particularly in the context of legal driving fitness evaluations under § 13 of the German Driving License Ordinance (FeV). Conventional approaches, such as self-reported drinking behavior, clinical interviews, and indirect biochemical markers like γ-glutamyltransferase (γ-GT) or carbohydrate-deficient transferrin (CDT), are limited by low sensitivity and high susceptibility to bias [1–3].

In recent years, direct ethanol biomarkers such as ethyl glucuronide (EtG) and phosphaditylethanol (PEth) have gained attention due to their higher specificity and ability to reliably reflect alcohol intake. EtG is a non-oxidative phase II metabolite of ethanol formed via conjugation with glucuronic acid. It can be measured in various matrices, including urine, blood, and hair. In blood, EtG reflects recent alcohol consumption within hours depending on the amount ingested and individual metabolism [3]. Compared to urine, blood EtG concentrations are less influenced by renal function or urine dilution, and may therefore provide a more controlled window of detection in forensic settings, if sensitivity is increased adequately [1].

PEth, in contrast, means a group of phospholipid homologues formed exclusively in the presence of ethanol through the action of phospholipase D. It accumulates in red blood cell membranes and reflects repeated or chronic ethanol exposure, providing a detection window of up to several weeks [4]. Especially PEth 16:0/18:1 is highly specific to ethanol and is considered one of the most sensitive biomarkers for long-term alcohol intake [3, 4].

In Germany, legally and medically relevant cut-off concentrations have been established to support forensic and traffic medicine evaluations. For EtG in urine, a threshold of 100 ng/mL is widely accepted to indicate recent consumption, whereas concentrations below 50 ng/mL are commonly used to confirm abstinence. A cutoff of 1 ng/mL for EtG in blood is considered comparable to the forensic threshold of 100 ng/ml in urine [5]. For EtG in whole blood, concentrations above 5 ng/mL are typically interpreted as indicative of recent alcohol intake [1]. For PEth, a concentration of ≥ 20 ng/mL is used to spot single to repeated alcohol consumption, while concentrations above 200 ng/mL may suggest harmful or chronic intake [6, 7]. In Germany, an upper cutoff of 210 ng/ml is recommended for forensic cases [8].

In forensic and traffic medicine practice, expert witnesses are occasionally confronted with cases where individuals present with markedly elevated blood alcohol concentrations (BAC). In such instances, defendants often claim that the elevated BAC stems from a single, exceptional drinking episode, as hints of alcohol abuse could jeopardize the driver’s license. However, BAC reflects only the acute, real-time ethanol level and does usually not provide retrospective insight into an individual’s habitual drinking behavior.

Schröck et al. [9] demonstrated that PEth and EtG provide complementary information in alcohol sober individuals, with PEth better suited to detect habitual alcohol use and EtG reflecting recent consumption. Their findings support the notion that a combined analysis of both markers could improve the differentiation of individual drinking patterns.

Against this background, the present study investigates the relationship between BAC, PEth, and EtG in blood samples collected primarily in the context of traffic offenses under the acute influence of alcohol. The aim was to evaluate whether alcoholised drivers/individuals are generally likely to be social or heavy drinkers.