What is AST?
AST is an enzyme from the metabolism of amino acids, and it sits wherever a lot of energy is converted: in your liver cells, in your skeletal muscles, in your heart muscle, and to a lesser extent in your kidneys and red blood cells. It leaks into your blood as soon as cells in one of those tissues are damaged. So the value says cells are under strain somewhere, and unlike ALT it does not immediately say where. That is why AST and ALT are always read together. ALT sits almost only in the liver; AST sits in the liver and in the muscles. If AST rises while ALT stays normal, it comes from the muscles, and in anyone who does sport that is the most common situation: a hard strength session or a long run lets AST double or triple for a few days without anything being wrong with the liver. If both rise, it is the liver, and if AST rises more than ALT with a high gamma-GT alongside, alcohol is the first suspect. In fatty liver it is the other way round: ALT sits higher than AST. Your report shows AST in U/L. Normal is up to about 35 U/L for a man from age 19 and up to 31 U/L for a woman; in men the limit sits higher because they have more muscle mass. AST disappears from the blood faster than ALT, in about a day, so a rise from training is gone after a few rest days.
Why is AST relevant?
For anyone who does sport, AST is the liver value that most often gives an unnecessary scare. After a hard session, a race or a new exercise the muscles leak enzymes, and AST then sits above the band for a few days, together with CK and LDH, while ALT and gamma-GT stay quiet. That is not liver but muscle recovery. Anyone who knows that has blood drawn on a rest day and reads the value in the right company; anyone who does not gets a liver work-up that leads nowhere. The second reason is alcohol. Alcohol damages the liver cells in a way that mainly frees AST, and it also depletes the vitamin B6 with which ALT is measured. So with regular drinking AST rises more than ALT, and a ratio of AST to ALT above 2 in a liver problem is the classic picture of alcohol. Together with a high gamma-GT and a high MCV that is a pattern that answers the question about drinking before you ask it, and it falls in the weeks after you cut down. The third reason is the same as with ALT: fatty liver, the most common liver condition, in which AST usually rises somewhat less than ALT. And because AST also sits in the heart muscle, it rises with damage to the heart, though that is measured with troponin nowadays and no longer with AST.
AST reference ranges
What counts beside the number:
- ALT from the same draw: normal ALT is muscle, high ALT is liver
- The ratio of AST to ALT: above 2 in a liver problem fits alcohol, below 1 fits fatty liver
- Gamma-GT, which goes up with alcohol and liver and stays normal with muscles
- CK, which shows muscle damage directly
- When you last trained hard
- How much you drink, and what you take
The bands above are where the labs overlap; the upper limit differs per lab and sits higher in men because muscles contain as much AST as the liver. There is no lower limit that means anything. More important than the limit is the company: a high AST with a normal ALT is muscle, and after hard training the value sits higher for a few days without anything being wrong.
What Dutch labs actually use
0 – 31U/L
Between 31 and 35 it depends on the lab, because each sets its limits on its own method and population. Above 35 every lab calls it abnormal.
every lab calls 0 – 31 U/L normal. Between 31 and 35 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Men 12–18 yrs | 22–52 U/L |
| Women 12–18 yrs | 19–42 U/L | |
| Men 19+ | 0–35 U/L | |
| Women 19+ | 0–31 U/L | |
| Star-shl2026 | Men | 0–35 U/L |
| Women | 0–31 U/L | |
| Certe2026 | Men from 18 yrs | < 35 U/L |
| Women from 18 yrs | < 31 U/L | |
| Clinical Diagnostics2026 | Men | < 50 U/L |
| Women | < 35 U/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
AST high or low: what it means
A high AST means cells under strain in liver, muscles or heart. In order of how often it occurs: hard training or muscle damage, fatty liver, alcohol, medicines or supplements, and rarely damage to the heart muscle or a viral hepatitis. The key is ALT beside it. High AST with normal ALT and normal gamma-GT is muscle; high AST and high ALT is liver; high AST that rises more than ALT, with high gamma-GT, is alcohol; high ALT that rises more than AST is fatty liver. A low AST means nothing. With little muscle mass or a vitamin B6 deficiency the value sits somewhat lower, and that is not a finding. What you do about it: with a rise after training you do nothing, except have blood drawn on a rest day next time. With fatty liver, weight loss is the lever, with less sugar and more exercise. With alcohol it is cutting down, and the value shows within weeks whether that worked. With a medicine or supplement you check whether the rise started with something new. Always read AST beside ALT and gamma-GT, and in an athlete beside CK, which shows muscle damage directly. Have blood drawn on a rest day, at least two days after hard exertion, and compare over time under the same conditions.
What lowers it
Rarely a finding; little leakage is simply little leakage.
| Cause | How often |
|---|---|
| Little muscle massMuscles supply part of the AST in your blood; with less muscle, especially in older people, the value sits somewhat lower | Sometimes |
| Vitamin B6 deficiencyThe enzyme needs B6 to work and is measured less well without it | Rare |
What raises it
Cells under strain, and the question is whether that is in the muscles, the liver or the heart.
| Cause | How often |
|---|---|
| Hard training or muscle damageAfter a hard strength session, a long run or a muscle injury the muscles leak AST; the value doubles or triples for a few days, with a normal ALT and gamma-GT | Often |
| Fatty liverThe most common liver cause; ALT then usually rises more than AST, with belly fat and high triglycerides alongside | Often |
| AlcoholMainly frees AST and hampers the measurement of ALT; AST raised more than ALT with a high gamma-GT is the classic picture of drinking | Often |
| Medication or supplementsParacetamol in high doses, some antibiotics, statins at the start and herbal preparations; check whether the rise started with something new | Sometimes |
| Heart muscle damageAST also sits in the heart muscle and rises with a heart attack; that is measured with troponin nowadays | Rare |
| Viral hepatitisGives a sharp rise of AST and ALT together, to many times the upper limit | Rare |
How does an AST blood test work?
- Referral
- Not needed. AST is in every liver panel you can have measured yourself, together with ALT and gamma-GT.
- Fasting
- Not needed. AST barely moves with what you eat.
- When
- On a rest day, at least two days after hard exertion, because muscles lift AST for a few days.
- The draw
- One tube of blood from a vein in your arm, which must not haemolyse, because red blood cells contain AST too. ALT and gamma-GT come from the same draw.
- Repeating
- After a rise from training a week later on a rest day; after a change in alcohol or medicines after six to twelve weeks.
- Which test
- AST is in the comprehensive test (€229) and in .
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What is AST?
An enzyme from the metabolism of amino acids that sits in your liver cells, but just as much in your skeletal muscles and your heart muscle. It leaks into your blood when cells in one of those tissues are damaged. That is the difference from ALT, which sits almost only in the liver, and the reason the two are always read together: ALT says liver, AST says liver or muscle.
What is a normal AST level?
Up to about 35 U/L for a man from age 19 and up to 31 U/L for a woman, where the labs overlap; the limit differs per lab. In men it sits higher because they have more muscle mass. More important than the limit is the combination with ALT and gamma-GT, and when you last trained hard.
What does a high AST mean?
That cells are under strain, in the muscles, the liver or the heart. With a normal ALT and gamma-GT it is muscle, usually after hard training. With a high ALT it is the liver, and then the ratio says more: ALT higher than AST is fatty liver, AST raised more than ALT with a high gamma-GT is alcohol. A sharp rise of both is an acute picture, usually a virus or a medicine.
Can my AST be too low?
No. Little AST in your blood means little leakage, and there is no lower limit that means anything. With little muscle mass or a vitamin B6 deficiency the value sits somewhat lower, and that is not a finding.
Can hard training raise my AST?
Yes, and considerably. After a hard strength session, a long run, a race or a new exercise the muscles leak AST, together with CK and LDH, and the value doubles or triples for a few days. ALT and gamma-GT stay quiet meanwhile, and that is how you recognise it. So have blood drawn on a rest day, at least two days after hard exertion, because otherwise you get a liver picture that leads nowhere.
What does the ratio between AST and ALT say?
Where a liver problem comes from. Alcohol mainly frees AST and hampers the measurement of ALT, so with regular drinking AST rises more than ALT and the ratio goes above 2, with a high gamma-GT and often a high MCV alongside. In fatty liver it is the other way round and ALT sits higher. The ratio only says something when one of the two is genuinely raised.
How do I lower a high AST?
By removing the cause. If it comes from the muscles, you do nothing and have blood drawn on a rest day next time. If it is the liver, it is weight loss with less sugar and more exercise in fatty liver, and cutting down with alcohol; in both cases the value falls within weeks. If the rise began with a new medicine or supplement, that is the first suspect.
Do I need to fast for an AST test?
No. AST barely moves with food. What does count: have blood drawn on a rest day, at least two days after hard exertion, and make sure the tube does not haemolyse, because red blood cells contain AST too. ALT and gamma-GT come from the same draw.
Which tests include AST?
AST is in the Liver function test (€59, also as an add-on for €15), in the comprehensive test (€229) and in .
Related biomarkers
Read on
Sources
- 1.Unilabs, test catalogue (Dutch): AST. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): AST. 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): AST. 2026. bepalingenwijzer.certe.nl
- 4.Clinical Diagnostics, lab guide (Dutch): AST. 2026. clinicaldiagnostics.nl
- 5.LESA Laboratory diagnostics (Dutch primary-care laboratory agreement). 2026. richtlijnen.nhg.org
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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