Elevated Blood Alcohol Levels Without Drinking: Diagnostic Approach

Primary Differential Diagnosis

The American Association for the Study of Liver Diseases recommends ruling out actual alcohol consumption first, as underreporting of alcohol use is extremely common, with 57.7% of patients underreporting their alcohol use when self-reported consumption is compared to objective biomarkers like phosphatidylethanol (PEth) 1
The European Association for the Study of the Liver notes that 28.6% of patients with presumed "non-alcoholic" liver disease actually had moderate or excessive alcohol use based on hair and urine ethyl glucuronide (EtG) testing 2
Objective biomarker testing is essential because patients frequently minimize or deny alcohol consumption, even when confronted with evidence, with a sensitivity of 91-100% and specificity of 77-96% for PEth 1, 3

The American College of Gastroenterology recommends using phosphatidylethanol (PEth) as the most reliable biomarker, detecting alcohol use over 10-14 days, with a cutoff >20 ng/mL indicating recent drinking 1, 3
Urinary Ethyl Glucuronide (EtG) and Ethyl Sulfate (EtS) can also be used, detecting alcohol use within 3 days, with a sensitivity of 76-89% and specificity of 86-99% 1, 3
Carbohydrate-Deficient Transferrin (CDT) has a half-life of 2-3 weeks, but has a major limitation of false positives in severe liver disease without alcohol use, and low sensitivity (25-50%) makes it less useful 1, 3, 5

Auto-brewery syndrome (gut fermentation syndrome) is the primary non-drinking cause, though extremely rare, and is characterized by endogenous ethanol production by gut microorganisms fermenting dietary carbohydrates 3
Diagnosis of auto-brewery syndrome requires documented elevated blood alcohol after supervised carbohydrate challenge with witnessed abstinence from alcohol, and is often associated with antibiotic use, diabetes, or conditions causing gut dysmotility 1, 4

The American Medical Association recommends obtaining objective biomarkers, such as PEth level (most reliable), and if PEth is unavailable, ordering urinary EtG/EtS, and never relying on patient self-report alone given the 57.7% underreporting rate 1, 3
If biomarkers are negative, consider auto-brewery syndrome if symptoms occur after carbohydrate-rich meals, and history of antibiotic use, diabetes, or gut dysmotility, and confirm with supervised carbohydrate challenge test with witnessed abstinence 1, 3