What laboratory tests should be checked in someone with heavy alcohol (ethanol) use?

Laboratory Testing for Heavy Alcohol Use

For patients with heavy alcohol use, obtain a comprehensive liver function panel including AST, ALT, GGT, alkaline phosphatase, bilirubin, albumin, and prothrombin time, along with a complete blood count to assess MCV, and screen for viral hepatitis (HCV, HBV) given the synergistic liver damage with alcohol. 1

Essential Liver Function Tests

The cornerstone of laboratory evaluation includes a full hepatic panel 2, 1:

• AST and ALT: An AST/ALT ratio >2 is highly suggestive of alcoholic liver disease, with ratios >3 being even more specific 1, 3. However, AST rarely exceeds 300 IU/L in pure alcoholic hepatitis—levels above this should prompt evaluation for alternative diagnoses 1.
• Gamma-glutamyl transpeptidase (GGT): The most widely used marker, detecting 34-85% of problem drinkers 1. GGT has 73% sensitivity for detecting daily ethanol consumption >50g, higher than AST (50%) or ALT (35%) 4. However, its lack of specificity limits utility as a standalone screening tool 2.
• Alkaline phosphatase, bilirubin, albumin, and prothrombin time: These assess for cholestasis and synthetic liver function 1.

Hematologic Assessment

• Mean corpuscular volume (MCV): Commonly elevated in chronic alcohol use, particularly when consumption exceeds 60g/day 2, 1. MCV normalizes slowly after several months of abstinence 3.
• Platelet count: May be decreased, indicating advanced liver disease or direct alcohol toxicity 1.
• Complete blood count: Neutrophilia may be present, particularly in alcoholic hepatitis 1.

Metabolic Panel

• A comprehensive metabolic panel including glucose, electrolytes, blood urea nitrogen, and creatinine should be performed 1, 3. This assesses for metabolic complications and helps rule out alternative diagnoses.

Viral Hepatitis Screening

This is critical and often overlooked:

• Hepatitis C (anti-HCV): Mandatory testing, as HCV and alcohol have a synergistic relationship resulting in more advanced liver disease than either alone 1.
• Hepatitis B (HBsAg and anti-HBc): Screen particularly in endemic populations 1.
• HIV (anti-HIV): Recommended in at-risk individuals, as 6-13% of HIV-infected persons are coinfected with HBV, affecting liver disease progression 1.

Enhanced Diagnostic Approach

Combining markers significantly improves detection:

• Using GGT and MCV together increases sensitivity for detecting alcohol abuse compared to either test alone 3, 5.
• Carbohydrate-deficient transferrin (%CDT) is the most specific marker (specificity 84-96%), with sensitivity of 41-66% depending on drinking severity 5, 6. When combined with GGT using a mathematically formulated equation, high sensitivity is reached without loss of specificity 5.
• %CDT provides the highest diagnostic performance (AUC 0.77) followed by GGT (AUC 0.68) for detecting excessive drinkers 6.

Additional Considerations

• Non-invasive fibrosis markers: Should be used to screen for advanced liver disease 1.
• Alpha-fetoprotein (AFP) and ultrasound: For hepatocellular carcinoma screening in high-risk patients 1.
• Ethyl glucuronide (EtG): In urine or hair can accurately monitor abstinence 1.

Critical Clinical Pitfalls

Laboratory testing alone is insufficient:

• Always combine with structured questionnaires: Patients routinely underreport consumption 1, 3. Use AUDIT (positive if ≥8 for men up to age 60, or ≥4 for women/adolescents/men >60) or CAGE questionnaires 2, 3.
• Normal labs don't exclude disease: 80-90% of heavy drinkers develop fatty liver, but laboratory abnormalities may be minimal or absent in early alcoholic liver disease 1. Biomarkers have imperfect sensitivity—even %CDT misses 34-59% of heavy drinkers 7.
• Don't rely on single biomarkers: Relying on one marker will miss many cases due to limited sensitivity 3. GGT loses specificity in advanced liver disease as it elevates regardless of etiology once extensive fibrosis develops 4.
• AST/ALT ratio >2 is uncommon in early disease: Only 2% of excessive drinkers without cirrhosis have AST/ALT >2, whereas 51% with alcoholic cirrhosis do—this ratio suggests advanced disease, not just heavy drinking 6.

Interpretation Context

• GGT may be elevated due to non-alcoholic causes including obesity, diabetes, medications (interferon, antipsychotics, beta-blockers, steroids), and other liver diseases 4, 3.
• MCV elevation requires several months of heavy drinking to develop and normalizes slowly with abstinence 3.
• Biomarkers are more likely to be elevated in those aged >30 years with longer drinking history 8.