ALT

Diagnostic Use

Common causes of raised plasma aminotransferases ALT and AST include

viral hepatitis
alcohol related hepatitis
non-alcoholic fatty liver disease (steatohepatitis)
toxic or ischaemic hepatitis.
Less common causes include

hemochromatosis
autoimmune hepatitis
Wilson’s disease
alpha-1 antitrypsin deficiency.

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.

ALT is more liver-specific than AST. 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 2 in alcoholic hepatitis.

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

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)
Note: The drugs sulfasalazine and sulfapyridine cause negative interference in the assay; patients on these drugs may have falsely low results . Additionally, iron infusions (such as ferric carboxymaltose ) interfere with testing and may give falsely low results or make AST & ALT unmeasurable . This effect appears to resolve rapidly (around 24hrs).

Reference Intervals

Units: U/L

Reference range:  0 – 45

Pregnancy: ALT falls by about 30% from pre-pregnant values. In patients with normal ALT values before pregnancy the upper reference limit in pregnancy will be 32 U/L.

ALT is more specific for liver cell damage than AST.