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22-25 AST, ALT

AST and ALT: liver enzymes, degrees of elevation and causes (fatty liver, hepatitis, alcohol, medicines), when to seek care.

Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are enzymes inside cells that transfer amino groups between amino acids. When cells are damaged, the enzymes leak into the blood. ALT is found mainly in the liver, so it is the more liver-specific marker. AST is also present in heart and skeletal muscle, kidneys, brain and red blood cells. Raised transaminases are the most common sign of liver cell injury, from fatty liver and hepatitis to medicines and alcohol.

Liver function testsHepatocellular injuryFatty liver

ALT — healthy upper limit (ACG)men 29–33, women 19–25 U/L

Usual lab upper limit≈ 35–55 U/L (method-dependent)

Marked rise> 15 × upper limit

UnitsU/L (older labs: other units)

Figure 1. Degree of transaminase elevation and typical causes. The pattern over time and the ratio to ALP matter as much as the absolute value.

Causes of raised transaminases

Group	Examples
Most common	Metabolic dysfunction-associated fatty liver disease (with obesity, diabetes, high triglycerides), alcohol, medicines and herbal or dietary supplements
Viral hepatitis	Hepatitis B and C (chronic), hepatitis A and E (acute), EBV, CMV
Other liver diseases	Autoimmune hepatitis, haemochromatosis, Wilson disease, alpha-1 antitrypsin deficiency, coeliac disease
Very high levels	Acute viral hepatitis, paracetamol or mushroom poisoning, ischaemic hepatitis ("shock liver"), acute bile duct obstruction
Outside the liver (mainly AST)	Intense exercise, muscle injury or disease, hypothyroidism, haemolysis; myocardial infarction

Reading the pattern

A predominant rise of ALT and AST compared with alkaline phosphatase (ALP) suggests hepatocellular injury. A predominant rise of ALP and bilirubin suggests cholestasis, impaired bile flow. The ratio AST/ALT (the De Ritis ratio) gives further clues: it is usually below 1 in fatty liver and viral hepatitis and often above 2 in alcoholic liver disease. A normal ALT does not exclude significant liver disease, including advanced fibrosis.

Seek urgent care

if raised transaminases come with jaundice (yellow skin or eyes), confusion, drowsiness, easy bruising, vomiting, abdominal pain, or after a possible overdose of paracetamol or other medicines.

Planned evaluation

Mildly raised values should be repeated and evaluated: alcohol intake, medicines and supplements, weight, hepatitis B and C tests, and an ultrasound of the liver. Avoid strenuous exercise for 48 hours before the test, because muscle work raises AST.

References

Kwo PY, Cohen SM, Lim JK. ACG clinical guideline: evaluation of abnormal liver chemistries. Am J Gastroenterol. 2017;112(1):18–35. doi:10.1038/ajg.2016.517
Botros M, Sikaris KA. The De Ritis ratio: the test of time. Clin Biochem Rev. 2013;34(3):117–130. PMID: 24353357

This article is for general information and does not replace a consultation with a doctor. Laboratory results must be interpreted by a physician together with symptoms and other tests.

Published on 30 April 2024