What labs should I order to verify alcohol intake?

Laboratory Tests for Verifying Alcohol Intake

The most effective laboratory approach to verify alcohol intake is to combine multiple biomarkers, particularly gamma-glutamyltranspeptidase (GGT), carbohydrate deficient transferrin (CDT), and direct alcohol markers such as ethyl glucuronide (EtG) and phosphatidylethanol (PEth). 1

Primary Laboratory Panel

Indirect Markers

1. Liver Function Tests

   • AST and ALT

     • AST/ALT ratio >2 suggests alcoholic liver disease
     • AST/ALT ratio >3 is highly suggestive of alcoholic etiology 1
     • AST typically elevated 2-6 times upper limit of normal
     • AST levels rarely exceed 300 IU/L in alcoholic hepatitis 1

   • Gamma-glutamyltranspeptidase (GGT)

     • Elevated in approximately 75% of habitual drinkers
     • Useful for monitoring abstinence as levels recover slowly after cessation 1
     • Limited specificity (can be elevated in non-alcoholic liver disease, obesity, diabetes, smoking) 1

   • Mean Corpuscular Volume (MCV)

     • Elevated with heavy drinking (especially >60g alcohol/day)
     • Returns to normal after several months of abstinence
     • Low sensitivity alone, but improved when combined with GGT 1

Direct Markers (Higher Specificity)

1. Ethyl Glucuronide (EtG)

   • Urine EtG (uEtG)

     • Detection window up to 80 hours after consumption
     • High sensitivity (89%) and specificity (99%) 1
     • Not affected by liver disease status

   • Hair EtG (hEtG)

     • Monitors long-term abstinence (up to 6 months)
     • Each 1cm segment reflects ~1 month of consumption
     • Internationally accepted cut-offs:
       • <7 pg/mg: abstinence
       • 7-30 pg/mg: social drinking

       • 30 pg/mg: excessive consumption (>60g ethanol/day) 1

2. Phosphatidylethanol (PEth)

   • Half-life of 10-14 days
   • Not affected by liver disease, kidney disease, age, BMI, or sex
   • High sensitivity (91-100%) and specificity (77-96%) 1
   • Cutoff of 80 ng/mL indicates ≥4 drinks/day
   • Cutoff of 20 ng/mL has excellent sensitivity for any alcohol use 1

3. Carbohydrate Deficient Transferrin (CDT)

   • High specificity but limited sensitivity (25-50%)
   • Requires daily intake of 50-80g ethanol for 1-2 weeks to be positive
   • Normalizes 2-3 weeks after abstinence
   • False positives can occur in severe liver disease 1

Optimal Testing Strategy

1. Initial Screening

   • GGT + AST/ALT ratio + MCV
   • These are widely available and inexpensive

2. Confirmation Testing

   • For recent consumption (days): urine EtG and/or PEth
   • For long-term monitoring (weeks to months): hair EtG and/or PEth

3. Combined Markers

   • GGT-CDT combined index provides better sensitivity (90%) than either marker alone 2

Important Considerations

• No single test is perfect - combining multiple markers significantly improves detection accuracy 1

• Time window matters:

  • Direct alcohol detection: hours
  • uEtG/EtS: 1-3 days
  • PEth: 2-4 weeks
  • hEtG: up to 6 months

• False positives/negatives:

  • Very low amounts of alcohol (<5g) can cause positive uEtG
  • Hair treatments (dying, bleaching) can reduce hEtG concentrations
  • CDT has false positives in severe liver disease
  • GGT lacks specificity (elevated in many conditions)

• Patient factors affecting results:

  • Women may have higher PEth levels for the same alcohol consumption
  • Renal failure can prolong EtG/EtS detection times
  • Slower hair growth in cirrhotic patients affects hEtG interpretation

Clinical Application

For the most comprehensive assessment of alcohol intake:

1. Order GGT, AST, ALT, and MCV as baseline tests
2. Add urine EtG for recent consumption verification
3. Consider PEth testing for a 2-4 week consumption window
4. For long-term monitoring, use hair EtG testing
5. Interpret results together rather than relying on any single test

This approach provides both immediate and historical information about alcohol consumption patterns, with direct markers offering the highest specificity for confirming intake.