By The Pawline veterinary teamVeterinary-reviewed by Alastair Greenway, BVM&S MRCVS · 25 July 2026
Reference range · U/L
050
Reference
0–50
Direction
Higher values are the concern.
This is the conventional reference interval. Your pet’s own report may print a slightly different range — always read the value against that. Sign in to see your pet’s value on this strip.
AST is an enzyme found in both liver and muscle, so it's read alongside ALT to judge whether a rise is coming from the liver or from muscle. When AST and ALT climb together it points to the liver; when AST rises with muscle markers, it points to muscle.
AST (aspartate aminotransferase, historically SGOT) is an enzyme that leaks into the blood when cells are damaged — but, unlike the more liver-specific ALT, it lives in significant amounts in two tissues: the liver and skeletal (and heart) muscle. That dual origin is the single most important thing to know about it. On its own, a raised AST cannot tell you whether the problem is hepatic or muscular; its job is to be read in combination with other enzymes to settle that question.
AST leaks from both liver and muscle, so it is read with ALT (liver) and CK (muscle) to decide which tissue a rise is coming from.
Reading a high result
A raised AST means cells are leaking the enzyme — from the liver, from muscle, or both. The way to localise it is the company it keeps:
AST up with ALT points to the liver, since ALT is liver-specific. AST tends to reflect somewhat more severe or acute hepatocellular injury, so a high AST alongside a high ALT can add a note about the intensity of the liver insult.
AST up with muscle markers (creatine kinase, CK) points to muscle — exertion, injury, inflammation of muscle, or even a difficult blood draw.
AST up with a normal ALT and normal CK is unusual and read in context.
So AST rarely changes the diagnosis by itself; it refines and corroborates what ALT (for liver) and CK (for muscle) are saying. A common practical use is spotting when a "liver" enzyme rise is actually partly muscular.
Reading a low or normal result
A normal AST is reassuring, and a low AST has no clinical significance. As with all the enzymes, a normal AST does not fully exclude liver disease — some chronic conditions run with normal enzymes — so it is read as part of the panel and the clinical picture.
In chronic disease
Followed over time, AST adds to the liver enzyme trend, and its behaviour relative to ALT can hint at the nature and severity of an ongoing process. Because it also reports on muscle, a persistently raised AST with normal liver markers can redirect attention to a muscle condition worth pursuing. Its value in monitoring is as a corroborating line alongside ALT rather than a lead marker.
Cat vs dog
AST is interpreted the same way in both species, with similar reference ranges. In both, its shared liver-and-muscle origin is the key caveat, and it is always read with ALT (and CK where muscle is suspected). Because a struggling or heavily exercised animal can raise AST through muscle alone, the circumstances of the sample are considered before a liver cause is assumed.
How it's measured
AST is measured on a routine chemistry panel, reported in U/L. Haemolysis (red-cell breakage in the sample) can raise it artefactually, so clean collection matters. It is interpreted alongside ALT, ALP and, where muscle is a question, creatine kinase. Read the value against your own report's range.
What to do next
A raised AST is a prompt to look at the company it keeps: with ALT for the liver, with CK for muscle. If the pattern points to the liver, it is worked up as part of the hepatic picture; if to muscle, that avenue is explored. Because AST straddles two tissues, it is never interpreted alone — its usefulness is entirely in the combination.
Reference ranges reflect conventional laboratory intervals. Always interpret against your own lab's printed range and your veterinary surgeon's judgement. A brighter optimal band is shown only where a published guideline defines one, and it is cited.
This page is educational and is not a diagnosis. Lab results are interpreted in the full clinical context by your veterinary surgeon; a single value rarely tells the whole story.
