Diagnostic Use
Part of liver function test and increased ALT levels are associted with hepatocellular damage.
ALT is more liver-specific than AST. ALT is usually increased more than AST in most hepatic conditions. However, AST/ALT ratio >1 can occur in chronic hepatitis, cirrhosis, haemolysis and classically AST is less than 300 U/L with AST/ALT ratio >2 in alcoholic hepatitis.
AST or ALT >3000 U/L are rare in viral hepatitis but common in both toxin ingestion (especially paracetamol) and ischaemia hepatic injury.
Interpretation
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.
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)
Reference Intervals
Reference range: 0 – 45 U/L
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.
Test Method
Test performed by: LabPlus Automation
Principle: Enzymatic
Reagents: Roche Assay
Analyser: Roche Cobas
Limitations / Interference
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).
Uncertainty of Measurement
10% at levels under 25 U/L.
4% at levels over 150 U/L.