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

This test looks at how much AST is in your blood. That is short for aspartate aminotransferase. See SGOT on an older report? That is exactly the same thing.

The AST enzyme belongs inside your cells. There it helps convert amino acids. As long as a cell is intact, it stays neatly inside. The moment liver cells are damaged, it leaks into your blood. 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. AST 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 ALT, it more often comes from muscle. Gamma-GT reacts to your bile flow, but not to muscle damage.

Want to know for sure whether your muscles are the source? Then CK is the value that points at it.

If your AST is raised, you want to know why. A raised AST has several different causes. Below they are ordered by how often they really occur. Not by how frightening they sound.

1. Exercise. This is by far number one. A hard session or a first class of something new damages muscle fibres. 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. An important detail: gamma-GT and bilirubin did not move with it. That is how you tell muscle from liver.

2. Heavy alcohol use. Drinking heavily on a regular basis raises AST. It also shifts the ratio with ALT. Is your AST more than twice your ALT? And is your gamma-GT up too? Then that is the classic alcohol pattern.

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

4. Medicines and supplements. Some medicines burden your liver straight away. Certain medicines only do so after weeks. Concentrated herbal extracts belong here too. Never stop something you were prescribed on your own. Do discuss your list.

5. The blood draw itself. Your red blood cells are full of AST. If cells rupture inside the tube, you measure too high. Nothing is actually wrong then.

Look at the magnitude as well. Are you more than ten times above the upper limit? Such a markedly raised result almost always comes from acute viral hepatitis. In conditions of the liver 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. 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. A result inside the normal range is not a clean bill of health. One measurement says less than the trend over time.

AST belongs to a liver panel. Your GP requests one for symptoms that could fit your liver. Also 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. If you do, you mostly measure your training.

Did you go hard shortly beforehand anyway? Say so at the draw. Have it repeated later. That beats being alarmed by a number you can explain yourself.

You do not need to fast for AST. Are other tests on your form? For glucose or cholesterol fasting may be needed. So check your whole request.

Does your value come back raised? Then 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.