What does the Aspartate Aminotransferase test measure?

Why is Aspartate Aminotransferase measured?

AST is a sensitive but non-specific marker of tissue injury. In the liver it is released in hepatocellular damage alongside ALT, but because it is also abundant in myocardium and skeletal muscle, an isolated AST rise may point to cardiac ischaemia, myositis, or haemolysis rather than hepatic disease. The AST:ALT ratio is central to interpretation — a ratio below one suggests steatotic liver disease, a ratio above two favours alcohol-related hepatocellular injury, and a ratio near or above one with very high absolute values is seen in acute ischaemic or toxic hepatitis. AST is therefore interpreted in tandem with ALT, CK, troponin, and the rest of the liver panel.

Reference ranges

Standard reference

Approximately 10–40 U/L, sex- and laboratory-specific.

Functional medicine optimal

Optimal thresholds mirror those for ALT in the hepatic context, with some sources favouring upper limits around 30–35 U/L; however, AST's presence in non-hepatic tissues means that 'optimal' varies by clinical question.

Units

U/L, µkat/L

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.