Alanine Aminotransferase

Alanine Aminotransferase (ALT), formerly called Serum Glutamate Pyruvate Transaminase (SGPT), is an intracellular enzyme mainly found in the liver.

It catalyzes the reaction:
Alanine + α-ketoglutarate → Pyruvate + Glutamate

1️⃣ Marker of Hepatocellular Injury (Most Important)

ALT is a specific indicator of liver cell damage because it is predominantly present in hepatocytes.

Elevated in:

• Acute viral hepatitis
• Drug-induced liver injury
• Toxic hepatitis
• Ischemic liver injury
• Fatty liver disease

🔎 Significance:

• Levels may rise 10–100 times normal in acute hepatitis.
• ALT rises earlier and is more liver-specific than AST.

2️⃣ Acute Viral Hepatitis

• ALT is markedly elevated.
• Peaks before jaundice appears.
• Falls gradually during recovery.

👉 ALT is more elevated than AST in most acute liver conditions.

3️⃣ Chronic Liver Disease

Moderate elevation in:

• Chronic hepatitis
• Cirrhosis
• Non-alcoholic fatty liver disease (NAFLD)

Levels are usually less than in acute hepatitis.

4️⃣ Alcoholic Liver Disease

• AST is usually higher than ALT.
• AST:ALT ratio > 2 suggests alcoholic liver disease.

5️⃣ Non-Hepatic Causes (Mild Elevation)

• Muscle injury
• Myocardial infarction (mild increase)
• Severe burns

However, ALT is much more specific for liver compared to AST.

6️⃣ Monitoring Role

ALT is used to:

• Monitor response to hepatitis treatment
• Assess drug hepatotoxicity
• Follow progression of liver disease

Normal Reference Range

ALT: ~7–56 IU/L (varies by lab)