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Alanine Aminotransferase

Blood Sciences Test


Clotted Blood

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Reference Range

  • Male 10 – 41
  • Female 10 – 33

Test Usage

Alanine aminotransferase is an enzyme involved in the transfer of an amino group from the amino acid, alanine, to alpha-ketoglutaric acid to produce glutamate and pyruvate. ALT is located primarily in liver and kidney, with lesser amounts in heart and skeletal muscle. Increased ALT activity is more specific for liver damage than increased aspartate aminotransferase (AST) activity. ALT is seldom increased in patients with heart or muscle disease in the absence of liver involvement. In healthy children, plasma ALT activity is lower than AST until 15 to 20 years of age. Thereafter, plasma ALT activity tends to be higher than AST activity until age 60, when the activities become roughly equal. The half-life of ALT in the circulation is 47 +/- 10 hours.

ALT activity in the liver is 3000 fold higher than in serum. Measurement of serum ALT activity is a good indicator of hepatocyte injury.

Disease Peak ALT
Peak Bilirubin Protime
Viral hepatitis 10 – 40 <1 <15 <3
Alcoholic hepatitis 2 – 8 >2 <15 1 – 3
Toxic injury >40 >1 early <5 >5 transient
Ischaemic injury >40 >1 early <5 >5 transient

X ULN = times upper limit of normal, Protime prolongation is number of seconds above ULN

  • The best ALT discriminant value for recognizing acute hepatic injury is 300 U/L.
  • ALT increases before & peak near onset of jaundice in viral hepatitis. Activity falls slowly, an average of 10% per day. ALT remains elevated 27 +/- 16 days.
  • ALT levels fluctuate between normal and abnormal in hepatitis C. 15 to 50% of patients with chronic hepatitis C have persistently normal ALT.
  • In uncomplicated alcoholic hepatitis, ALT values are almost never >10 times the upper reference limit.
  • Extremely elevated ALT levels are common in toxic hepatitis and hepatic ischemia secondary to circulatory collapse and heatstroke. 90% of cases with ALT >3000 U/L are due to toxic or ischemic injury. AST is usually higher than ALT and both enzymes peak in the first 24 hours after admission. After peaking, both levels fall rapidly; AST faster than ALT.
  • Peak ALT levels bear no relationship to prognosis and may fall with worsening of the patients condition. In fulminant hepatic necrosis, decreasing ALT may signify a paucity of viable hepatocytes rather than recovery.

Patients with cirrhosis, non-alcoholic steatohepatitis, cholestatic liver disease, fatty liver and hepatic neoplasm typically have slightly raised serum ALT levels ( < 120 U/L). Patients with cirrhosis seldom have ALT levels higher than two times normal. Cirrhotic patients without ongoing liver injury the values may have normal values.

Other causes of elevated ALT include haemochromatosis, Wilson disease, autoimmune hepatitis, primary biliary cirrhosis, sclerosing cholangitis and alpha-1 antitrypsin deficiency. The medications most commonly associated with elevated ALT are sulfonamides, statins and isoniazid.

Helpful articles:

Pratt & Kaplan, NEJM 2000; 342: 1266-71 Evaluation of abnormal liver-enzyme results in asymptomatic patients

Dufour et al., Clin Chem 2000; 46: 2050-68 Diagnosis and monitoring of hepatic injury. II. Recommendations for use of laboratory tests in screening, diagnosis, and monitoring

Turnaround Time

1 day



Can be added on to an existing request up to 4 days following sample receipt


Please note this test is not UKAS accredited

Specimen Labelling Procedure
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