AST value: what does it mean on your blood test?

This test looks at how much AST is in your blood, in units per litre (u/l). AST is short for aspartate aminotransferase, and if you see SGOT on an older report, that is exactly the same thing. The enzyme belongs inside your cells, where it helps convert amino acids, the building blocks of protein. As long as a cell is intact, it stays neatly inside; the moment cells are damaged, it leaks into your blood, and the more cells break, the more of it you measure.

Now the point where explanations usually go wrong: AST is not only in your liver. It also comes from your skeletal muscle and your heart muscle, and from your kidneys, your brain and your red blood cells. The test cannot see where it came from; it only adds up.

That is why your GP almost never requests this on its own. On your blood test it usually sits next to ALT, gamma-GT, alkaline phosphatase and bilirubin. ALT is far more concentrated in your liver and is therefore more specific: if your AST is higher than your ALT, it more often comes from muscle. Gamma-GT reacts to your bile flow but not to muscle damage. And if you want to know for sure whether your muscles are the source, CK is the value that points at it, because it comes almost exclusively from muscle.

The normal range runs to 35 u/l in men and to 31 u/l in women; that difference comes from muscle mass and says nothing about the liver. Labs differ a little, so the range next to your own result is the one that counts.

If your AST is raised, you want to know why. Below the causes are ordered by how often they really occur, and not by how frightening they sound.

One: exercise. This is by far number one. A hard session or a first class of something new damages muscle fibres, and a long downhill walk does the same; AST is released in the process. In untrained people the value was still raised seven days after one heavy session, and an important detail: gamma-GT and bilirubin did not move with it. That is how you tell muscle from liver.

Two: heavy alcohol use. Drinking heavily on a regular basis raises AST and also shifts the ratio with ALT. If your AST is more than twice your ALT and your gamma-GT is up too, that is the classic alcohol pattern.

Three: fatty liver. Common, and usually the reason behind a mildly raised result without symptoms. Here ALT is higher than AST at first, and only as more scar tissue forms does that ratio flip.

Four: medicines and supplements. Some medicines burden your liver straight away, certain medicines only after weeks, and concentrated herbal extracts count as well. Never stop something you were prescribed on your own, but do discuss your list.

Five: the blood draw itself. Your red blood cells are full of AST, and if cells rupture inside the tube, you measure too high while nothing is actually wrong.

Look at the magnitude as well. If you are more than ten times above the upper limit, such a markedly raised result almost always comes from acute viral hepatitis, and in liver conditions such as hepatitis, values stay raised for months. What you do not see on this list is a heart attack: this test used to be used for that, and troponin took that role over long ago.

Ask your GP when AST should be checked again. If AST and ALT are both raised, a repeat usually follows first. One measurement says less than the trend over time, and a result inside the normal range is no clean bill of health.

AST belongs to a liver panel. Your GP requests one for symptoms that could fit your liver, to monitor medicines that burden it, or as part of a broader check.

There is one rule that genuinely matters: do not train hard in the 48 to 72 hours before your blood draw. No new class, no race, no heavy leg day, because otherwise you mostly measure your training. If you did go hard shortly beforehand, say so at the draw and have it repeated later; that beats being alarmed by a number you can explain yourself.

You do not need to fast for AST, but for glucose or cholesterol on the same form fasting may be needed, so check your whole request.

If your value comes back raised, the next step is not another AST test. Look at ALT, gamma-GT and CK instead; those three together usually point to where the enzyme came from. Always discuss an abnormal result with your GP.