What could cause a high blood alcohol level in the absence of alcohol consumption?

Elevated Blood Alcohol Without Drinking: Auto-Brewery Syndrome and Other Causes

The most important cause of elevated blood alcohol levels without drinking is auto-brewery syndrome (gut fermentation syndrome), though this is extremely rare; however, the far more common clinical scenario involves underreporting of alcohol use, which should be systematically ruled out first using objective biomarkers before considering rare metabolic conditions.

Primary Differential: Rule Out Actual Alcohol Consumption First

The evidence strongly indicates that underreporting of alcohol use is extremely common and must be excluded before considering rare causes:

• Studies show 57.7% of patients underreport their alcohol use when self-reported consumption is compared to objective biomarkers like phosphatidylethanol (PEth) 1
• In European studies, 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 1
• Objective biomarker testing is essential because patients frequently minimize or deny alcohol consumption, even when confronted with evidence 1

Recommended Biomarker Testing Algorithm

To definitively exclude alcohol consumption, use the following hierarchy 1:

1. Phosphatidylethanol (PEth) - Most reliable

   • Detects alcohol use over 10-14 days 1
   • Sensitivity 91-100%, specificity 77-96% 1
   • Not affected by liver disease, kidney disease, age, or BMI 1
   • Cutoff >20 ng/mL indicates recent drinking 1

2. Urinary Ethyl Glucuronide (EtG) and Ethyl Sulfate (EtS)

   • Detects alcohol use within 3 days 1
   • Sensitivity 76-89%, specificity 86-99% 1
   • Caution: Detection window prolonged in renal failure 1

3. Carbohydrate-Deficient Transferrin (CDT)

   • Half-life 2-3 weeks 1
   • Major limitation: False positives occur in severe liver disease without alcohol use 1
   • Low sensitivity (25-50%) makes it less useful 1

True Causes of Elevated Blood Alcohol Without Drinking

Auto-Brewery Syndrome (Gut Fermentation Syndrome)

This is the primary non-drinking cause, though extremely rare:

• Endogenous ethanol production by gut microorganisms (typically Candida species or Saccharomyces cerevisiae) fermenting dietary carbohydrates
• Patients present with signs of intoxication after consuming carbohydrate-rich meals
• Often associated with antibiotic use, diabetes, or conditions causing gut dysmotility
• Diagnosis requires: Documented elevated blood alcohol after supervised carbohydrate challenge with witnessed abstinence from alcohol

Toxic Alcohol Ingestions (Mimics, Not True Ethanol)

These cause elevated osmolal gap but not elevated ethanol levels 2:

• Methanol - Causes high anion gap metabolic acidosis, visual disturbances 2
• Ethylene glycol - Causes high anion gap acidosis, acute renal failure, calcium oxalate crystals 2
• Isopropanol - Causes hyperosmolality without acidosis, acetone breath 2
• These require fomepizole or ethanol treatment to inhibit alcohol dehydrogenase 2

Critical distinction: These toxic alcohols increase osmolal gap but are not detected as ethanol on standard blood alcohol testing 2

Clinical Approach Algorithm

Step 1: Obtain Objective Biomarkers

• Order PEth level (most reliable) 1
• If PEth unavailable, order urinary EtG/EtS 1
• Never rely on patient self-report alone given 57.7% underreporting rate 1

Step 2: If Biomarkers Negative

• Consider auto-brewery syndrome if:
  • Symptoms occur after carbohydrate-rich meals
  • History of antibiotic use, diabetes, or gut dysmotility
  • Confirm with supervised carbohydrate challenge test with witnessed abstinence

Step 3: Rule Out Laboratory Error

• Repeat blood alcohol level
• Ensure proper specimen handling (some hand sanitizers contain alcohol and can contaminate samples)
• Verify chain of custody if medicolegal implications

Step 4: Evaluate for Toxic Alcohol Ingestion

• Check serum osmolal gap and anion gap 2
• If elevated osmolal gap with high anion gap acidosis, consider methanol or ethylene glycol 2
• Urgent treatment with fomepizole indicated if toxic alcohol suspected 2

Common Pitfalls to Avoid

• Never accept patient denial of alcohol use without objective biomarker confirmation - 57.7% underreport consumption 1
• Do not use GGT or CDT alone - GGT elevated in 75% of drinkers but also in obesity, diabetes, and medications; CDT has false positives in severe liver disease 1, 3
• Do not confuse toxic alcohols with ethanol - they cause osmolal gap but are not detected as ethanol on standard testing 2
• Auto-brewery syndrome is extremely rare - exhaust common causes (underreporting, laboratory error) first before pursuing this diagnosis

Key Takeaway

In clinical practice, elevated blood alcohol without reported drinking is almost always due to underreporting rather than rare metabolic conditions 1. The priority is obtaining objective biomarkers (PEth preferred) to document actual alcohol exposure before considering exotic diagnoses like auto-brewery syndrome.