What does it mean if Aspartate Aminotransferase (AST) (SGOT) is elevated and Alanine Aminotransferase (ALT) (SGPT) is normal?

Elevated AST (SGOT) with Normal ALT (SGPT): Diagnostic Approach

When AST is elevated but ALT remains normal, this pattern strongly suggests a non-hepatic source of AST elevation, most commonly from cardiac or skeletal muscle injury, rather than primary liver disease. 1

Understanding the Pattern

AST is found in multiple tissues including cardiac muscle, skeletal muscle, kidneys, and red blood cells, which explains why elevations can occur without liver involvement. 1 In contrast, ALT is highly specific for liver injury due to its predominant concentration in hepatocytes with minimal presence in other tissues. 2, 1

When true hepatocellular injury exists, both ALT and AST typically rise together, with ALT usually being equal to or greater than AST (AST/ALT ratio <1). 2, 1 The isolated elevation of AST with truly normal ALT is therefore inconsistent with typical liver disease patterns.

Most Common Causes to Evaluate

Muscle Injury (Most Likely)

• Measure creatine kinase (CK) first before pursuing any liver-specific workup. 1 Elevated CK confirms skeletal or cardiac muscle as the origin of AST elevation. 2, 1
• Recent strenuous exercise, muscle trauma, or cardiac events can all elevate AST without affecting ALT. 2

Thyroid Disorders

• Check thyroid function tests (TSH, free T4) to exclude hypothyroidism, which can cause isolated AST elevation. 1, 3

Hemolysis

• AST is present in red blood cells, so hemolysis can elevate AST levels. 2

Important Exception: Alcoholic Liver Disease

An AST/ALT ratio >2 (especially >3) is highly suggestive of alcoholic liver disease, occurring in approximately 70% of alcoholic hepatitis cases. 1, 4 However, if ALT is truly normal, alcoholic liver disease is unlikely to be the sole cause. 1

• Quantify alcohol consumption using the AUDIT questionnaire—a score ≥8 warrants further evaluation. 1, 3
• If significant alcohol use is present and AST/ALT ratio >2, alcoholic liver disease becomes more likely despite "normal" ALT. 1

Critical Pitfall to Avoid

Verify that ALT is truly normal by checking sex-specific reference ranges: 29-33 IU/L for males and 19-25 IU/L for females. 2, 1 What appears "normal" by laboratory standards may actually represent mild elevation, particularly in women. 1

Recommended Diagnostic Algorithm

1. Repeat AST and obtain complete liver panel (ALT, alkaline phosphatase, GGT, total and direct bilirubin, albumin, PT/INR) within 1-2 weeks to verify the pattern. 1, 3

2. Measure creatine kinase (CK) to rule out skeletal or cardiac muscle injury as the primary cause. 1

3. Check thyroid function tests (TSH, free T4) to exclude hypothyroidism. 1, 3

4. Assess alcohol consumption using validated screening tools (AUDIT questionnaire). 1, 3

5. If CK is normal, thyroid function is normal, and no significant alcohol use:

   • Consider hemolysis as a cause 2
   • Evaluate for other extrahepatic sources of AST 1

When to Pursue Hepatology Referral

• AST remains elevated >6 months without identified cause 1
• Evidence of synthetic dysfunction develops (low albumin, elevated INR, elevated bilirubin) 1
• AST increases to >5× upper limit of normal 1

Key Takeaway

AST alone is insufficient to diagnose or monitor liver disease without corresponding ALT elevation. 1 The isolated elevation of AST with normal ALT should prompt evaluation for non-hepatic causes—particularly muscle injury—before attributing the elevation to liver pathology.