Alanine Aminotransferase (Blood)

Diagnostic Use

Common causes of raised plasma aminotransferases ALT and AST include:

• Viral hepatitis
• Alcohol related hepatitis
• Metabolic dysfunction associated steatotic liver disease (MASLD)
• Toxic or ischaemic hepatitis.

Less common causes include:

• Haemochromatosis
• Autoimmune hepatitis
• Wilson’s disease
• Alpha-1 antitrypsin deficiency.

When raised aminotransferase is apparently unexplained, several “non-hepatic” conditions may be considered:

• Coeliac disease
• Adrenal glucocorticoid deficiency e.g. Addison’s disease
• Muscular dystrophies (check CK)
• Macro-ALT or macro-AST (these are complexes with immunoglobulins, leading to slow clearance of the enzyme; contact laboratory to arrange evaluation)
• Thyroid dysfunction (hyper or hypo)
• Sleep apnoea-related disorder (can be associated with or independent of obesity/metabolic syndrome)

ALT is more liver-specific than AST and has a longer half life (around 47hrs) in circulation than AST (half life around 17hrs). Asymptomatic hepatitis carriers usually have normal levels. ALT is usually increased more than AST in most hepatic conditions. However, AST/ALT >1 can occur in chronic hepatitis, cirrhosis, haemolysis and classically AST is <300U/L with AST/ALT >2 in alcoholic hepatitis.

AST or ALT >3000U/L is rare in viral hepatitis but common in both toxin ingestion (especially paracetamol) and ischaemic hepatic injury.

Patients with cholestatic liver disease, cirrhosis or hepatic carcinoma can have normal or mildly raised aminotransferase activity.

Acute biliary obstruction occasionally can cause an early, transient and significant rise in aminotransferase level.

Reference Intervals