What blood test is done for diagnosing alcohol intoxication?

Blood Tests for Alcohol Intoxication

Blood alcohol concentration (BAC) measurement via venous blood sample is the gold standard test for diagnosing alcohol intoxication, though breath testing provides a reliable non-invasive alternative for screening purposes. 1

Primary Diagnostic Tests

Blood Testing

• Blood Alcohol Concentration (BAC):
  • Most accurate method for determining alcohol intoxication
  • Typically measured by automated enzymatic analysis of venous blood samples
  • Best correlated with level of impairment and clinical manifestations
  • Detects alcohol use within 2-12 hours of consumption
  • Considered the gold standard for both clinical and legal purposes 1
  • Drawbacks: invasive, requires trained personnel, more costly than alternatives 2

Breath Testing

• Breath Alcohol Concentration (BrAC):
  • Non-invasive alternative to blood testing
  • Provides rapid results (within minutes)
  • Good proxy for blood alcohol concentrations
  • Commonly used in emergency departments and by law enforcement
  • Excellent correlation with blood testing (r=0.95) when using appropriate conversion factors 3
  • Modern infrared breath analyzers provide reliable screening results
  • Less invasive than blood testing and requires minimal training 2, 3

Secondary Biomarkers

While not used for acute intoxication diagnosis, these markers help detect chronic alcohol use:

• Direct Alcohol Metabolites:

  • Phosphatidylethanol (PEth): Most sensitive and specific biomarker

    • Detects single drinking episode for up to 12 days
    • Measures chronic heavy use for up to 6 weeks
    • Directly correlates with amount of alcohol consumed 2

  • Ethyl Glucuronide (EtG) and Ethyl Sulphate:

    • Detectable in blood and hair for up to 3 days
    • More commonly assessed in urine 2

• Indirect Markers:

  • Gamma-glutamyltransferase (GGT)

  • Mean corpuscular volume (MCV)

  • Carbohydrate-deficient transferrin (CDT)

  • AST/ALT ratio (>2 suggestive of alcoholic liver disease) 4

  • These markers have limited sensitivity and many patients with alcohol misuse present normal results 2

Clinical Application Algorithm

1. For acute intoxication assessment:

   • Obtain venous blood sample for BAC measurement (gold standard)
   • Consider breath testing as a rapid screening alternative if available
   • Interpret results alongside clinical presentation

2. For suspected chronic alcohol use:

   • Consider PEth testing (most reliable biomarker)
   • AST/ALT ratio >2 suggests alcoholic liver disease
   • Complete liver panel including GGT, alkaline phosphatase, bilirubin, albumin, and PT/INR 4

Important Considerations

• Biomarkers should not replace a thorough clinical assessment and interview 2
• The AUDIT or AUDIT-C questionnaire is more effective than biomarkers for detecting alcohol misuse 2
• No single biomarker has perfect sensitivity and specificity
• PEth levels of 20-200 ng/ml may indicate moderate alcohol use (20-60g/day), while levels >200 ng/ml suggest heavier consumption 2

Pitfalls to Avoid

• Don't rely solely on indirect markers (GGT, MCV) for diagnosis of alcohol intoxication as they lack specificity
• Avoid using salivary reagent strips for quantitative BAC measurement as they have shown poor reliability (r=0.418) 5
• Don't substitute biomarker testing for a medical interview 2
• Remember that breath testing may be affected by recent use of alcohol-containing mouthwash or breath sprays 2