Laboratory Tests for Evaluating Suspected Alcohol Abuse
The most effective laboratory approach for evaluating suspected alcohol abuse includes a combination of liver function tests (AST, ALT, GGT) and complete blood count (particularly MCV), as no single test provides adequate sensitivity or specificity. 1, 2
Primary Laboratory Tests
- AST/ALT ratio: An AST/ALT ratio >2 is highly suggestive of alcoholic liver disease, and ratios >3 are even more specific for alcoholic etiology 1, 3
- Gamma glutamyl transpeptidase (GGT): Commonly elevated in alcohol users, but has limited sensitivity and specificity when used alone 1
- Mean corpuscular volume (MCV): Elevated in chronic alcohol users, particularly when consumption exceeds 60g/day 2, 4
- Complete metabolic panel: To assess for other liver abnormalities and rule out alternative diagnoses 1
Enhanced Diagnostic Approach
- Combined markers: Using GGT and MCV together significantly improves sensitivity for detecting alcohol abuse compared to either test alone 2, 5
- Carbohydrate-deficient transferrin (CDT): More specific but has limited sensitivity and is affected by age, sex, BMI, and other liver diseases 1, 5
- GGT-CDT combination: Has shown superior sensitivity (90%) compared to individual markers (CDT: 63%, GGT: 58%, MCV: 45%) 5
Interpreting Laboratory Results
- AST levels in alcoholic hepatitis typically range from 2-6 times the upper limit of normal 1, 3
- AST levels >500 IU/L or ALT >200 IU/L are uncommon in alcoholic hepatitis and suggest another etiology 1, 3
- GGT may be elevated due to non-alcoholic causes including obesity, diabetes, smoking, or medication use 2, 4
- Normal laboratory values do not exclude significant alcohol use or alcoholic liver disease 3, 6
Clinical Correlation
- Laboratory tests should be used alongside validated screening questionnaires such as AUDIT or CAGE for improved detection 1, 4
- The AUDIT questionnaire is considered positive with scores ≥8 for men up to age 60, or ≥4 for women, adolescents, or men over 60 1
- Laboratory markers are particularly useful when patient history is unreliable or unavailable 4, 6
Common Pitfalls
- Relying on a single biomarker will miss many cases of alcohol abuse due to limited sensitivity 1, 5
- High AST/ALT ratios may indicate advanced alcoholic liver disease rather than simply heavy drinking 7
- GGT loses specificity in advanced liver disease 3, 8
- Laboratory tests may be influenced by non-alcohol-related diseases, enzyme-inducing drugs, nutritional factors, and metabolic disorders 8, 6