What is AST?

Name: AST
Creator: Dr Robin Wang

Written by Dr Robin Wang

AST is an enzyme that sits inside cells and appears in blood when those cells are damaged. Liver cells contain it, but so do heart muscle, skeletal muscle and red blood cells, and the enzyme released from each looks identical in a blood sample.

Test your AST See related biomarkers

Why does AST matter?

AST is grouped with the liver tests, but the liver is only one of its sources. A rise can come from muscle or from red cells breaking down while the liver is untouched, so AST registers damage without locating it.

How does AST relate to other markers?

ALT is confined almost entirely to liver cells, so measuring the two enzymes together separates liver injury from injury elsewhere. Red blood cells carry AST of their own, so Haemoglobin is read next to AST to check whether the breakdown of those cells, rather than the liver, is what released it.

What affects AST?

Strenuous exercise and muscle injury release AST from skeletal muscle, and injury to heart muscle does the same from cardiac tissue. Alcohol and viral infection act on the liver cells themselves, injuring them so the enzyme leaks out.

Why Do Health tests AST three times a year

AST rises within hours of injury to muscle, heart or liver, then falls over one to two weeks as the tissue repairs and the enzyme is cleared. A single measurement can land anywhere in that window without saying which tissue put it there. Testing about every four months shows whether a change persists or belonged to one bout of exertion or illness. This is Do Health's monitoring schedule, not a general recommendation for everyone.