What is ALT?
Your liver is a factory of a kilo or so that processes everything that comes out of your gut: sugars, fats, proteins, alcohol, medicines. ALT, alanine aminotransferase, is one of the enzymes the liver cells use to do that, and it sits almost exclusively in those cells. As long as they are intact, it stays inside. If they become damaged, inflamed or overfull with fat, ALT leaks into the bloodstream and the value rises. So ALT is not a measure of how well your liver works, but of whether cells are under strain. It is the most sensitive of the ordinary liver values, and at the same time the least specific about the cause. Fatty liver, alcohol, a virus, a medicine and a hard training session all give the same thing: a higher number. The pattern with the other liver values points the way. If AST rises more than ALT, the muscles or alcohol are more likely; if gamma-GT rises with it, it is the liver; if ALP and bilirubin rise with it, it sits in the bile drainage. Your report shows ALT in U/L. Normal is up to about 45 U/L for a man from age 19 and up to 34 U/L for a woman. A healthy liver sits well below that, and the value moves within weeks with what you eat, drink and do.
Why is ALT relevant?
ALT is the value by which you see fatty liver before you notice anything of it, and fatty liver is by now the most common liver condition in the Netherlands: in roughly one in four adults there is fat in the liver that does not belong there. It gives no symptoms, not for years. It goes together with belly fat, insulin resistance, a high triglyceride level and a low HDL, and it is a forerunner of diabetes and cardiovascular disease. A slightly raised ALT in someone otherwise healthy is nine times out of ten this, and it is fully reversible. That reversing is exactly where ALT has its value. Fat leaves the liver with weight loss, less sugar and refined carbohydrates, less alcohol and more exercise, and ALT falls with it within weeks. A liver that is clean again recovers completely. Anyone who sees a raised ALT and three months later a normal one has achieved something you do not see from the outside but that makes a difference of years. Coffee helps too: two to three cups a day go together with less fatty liver and less scarring. The other reasons are worth ruling out. Alcohol lifts ALT, usually together with a higher gamma-GT and an AST that rises more than ALT. Medicines and supplements do it too: paracetamol in high doses, some antibiotics, statins at the start, and herbal preparations such as green tea extract and kava. A viral hepatitis usually gives a sharp rise. And rarer are iron overload, coeliac disease and an autoimmune inflammation of the liver, which can be recognised with a few extra values.
ALT reference ranges
What counts beside the number:
- AST and gamma-GT: if AST rises more, muscles or alcohol; if gamma-GT rises with it, the liver
- ALP and bilirubin, which go up with it in a problem of the bile drainage
- Your waist, triglycerides, HDL and fasting glucose, the company of fatty liver
- How much you drink, and what you take in medicines and supplements
- Whether you trained hard in the days before
- How high: up to one and a half times the upper limit is usually lifestyle, ten times or more is acute
The bands above are where the labs overlap; the upper limit differs by a few units per lab and sits lower in women than in men. More important than the limit itself is how far above it you sit: up to one and a half times is in someone without symptoms usually lifestyle, a few times is repeated, and ten times or more is acute. A healthy liver sits well below the upper limit, and the value moves within weeks with weight, alcohol and medicines.
What Dutch labs actually use
0 – 34U/L
Between 34 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 – 34 U/L normal. Between 34 and 35 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Men 13–18 yrs | 0–31 U/L |
| Women 13–18 yrs | 0–29 U/L | |
| Men 19+ | 0–45 U/L | |
| Women 19+ | 0–34 U/L | |
| Star-shl2026 | Men | 0–45 U/L |
| Women | 0–34 U/L | |
| Certe2026 | Men 18+ | < 45 U/L |
| Women 18+ | < 34 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.
ALT high or low: what it means
A high ALT means liver cells under strain. From common to rare: fatty liver, alcohol, medicines or supplements, hard training in the days before, and rarely a viral hepatitis, iron overload, coeliac disease or an autoimmune inflammation. A slightly raised value, up to one and a half times the upper limit, is in someone without symptoms usually lifestyle and falls with it; a value of a few times the upper limit should be repeated; a value of ten times the upper limit or more is an acute picture, usually a virus or a medicine, and then the day counts. A low ALT means nothing. In older people with little muscle mass or with a vitamin B6 deficiency the value sits somewhat lower, and that is not a finding. What you do about it: with a slightly raised ALT and belly fat, weight loss is the lever, and a few kilos is already enough to clear the liver of fat; besides that less sugar, soft drinks and white bread, less alcohol, more exercise, and coffee is fine. If you drink regularly, try a month without and have blood drawn again: if ALT falls, you know what it was. If you take something new, check whether the rise started with it. Count on six to twelve weeks before the value shows the new balance. Set ALT beside AST, gamma-GT, ALP and bilirubin, and with a rise beside your triglycerides, HDL and fasting glucose, because those tell whether it is the fat metabolism. Do not have blood drawn in the days after hard training, and compare over time at the same lab.
What lowers it
Rarely a finding; little leakage is simply little leakage.
| Cause | How often |
|---|---|
| Little muscle massEspecially in older people; there is some ALT in muscles too, and with less muscle the value sits somewhat lower | Sometimes |
| Vitamin B6 deficiencyThe enzyme needs B6 to work and is measured less well without it; with alcohol and one-sided eating | Rare |
What raises it
ALT is leaking from liver cells under strain, and the question is why.
| Cause | How often |
|---|---|
| Fatty liverThe most common reason in anyone otherwise healthy; goes together with belly fat, high triglycerides and insulin resistance, and is fully reversible with weight loss and less sugar | Often |
| AlcoholLifts ALT, usually with a higher gamma-GT and an AST that rises more than ALT; a month without lets it fall | Often |
| Medication or supplementsParacetamol in high doses, some antibiotics, statins at the start, and herbal preparations such as green tea extract and kava; check whether the rise started with something new | Sometimes |
| Hard training shortly before the drawMuscles contain some ALT too and plenty of AST; after a hard session both sit higher for a few days | Sometimes |
| Viral hepatitisHepatitis A, B, C or E usually give a sharp rise, to many times the upper limit, often with tiredness and dark urine | Rare |
| Iron overload, coeliac disease or an autoimmune inflammationRarer, and recognisable with ferritin and transferrin saturation, antibodies against gluten and autoantibodies | Rare |
How does an ALT blood test work?
- Referral
- Not needed. ALT is in every liver panel you can have measured yourself, together with AST, gamma-GT, ALP and bilirubin.
- Fasting
- Not needed. ALT barely moves with what you eat.
- When
- Not in the days after hard training, and preferably not just after a weekend with plenty of alcohol, unless you want to see exactly what that does.
- The draw
- One tube of blood from a vein in your arm. The other liver values and your fat metabolism come from the same draw.
- Repeating
- Six to twelve weeks after a change in weight, alcohol or medicines to see whether the value falls with it; a sharply raised value is repeated within days.
- Which test
- ALT 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 ALT?
An enzyme that sits almost exclusively in your liver cells and that they use to process proteins. As long as the cells are intact, it stays inside; if they become damaged, inflamed or overfull with fat, it leaks into your blood. ALT is therefore not a measure of how well your liver works, but of whether liver cells are under strain, and it is the most sensitive ordinary liver value.
What is a normal ALT level?
Up to about 45 U/L for a man from age 19 and up to 34 U/L for a woman, where the labs overlap; the limit differs by a few units per lab. A healthy liver sits well below that. More important than the limit is how far above it you sit: up to one and a half times is usually lifestyle, ten times or more is acute.
What does a high ALT mean?
That liver cells are under strain. In anyone otherwise healthy that is nine times out of ten fatty liver: fat in the liver from belly fat, sugar and too little exercise, which gives no symptoms and is fully reversible. After that alcohol, medicines and supplements, and hard training in the days before. A sharply raised value, many times the upper limit, is usually a virus or a medicine and is repeated within days.
What does a low ALT mean?
Nothing. Little ALT in your blood means little leakage. In older people with little muscle mass or with a vitamin B6 deficiency the value sits somewhat lower, and that is not a finding; the test exists to find a rise.
What is fatty liver and how do I get rid of it?
Fat that builds up in the liver cells when more sugar and fat comes in than the liver can get rid of, usually with belly fat and insulin resistance. It occurs in about one in four adults, gives no symptoms for years and is a forerunner of diabetes and cardiovascular disease. It disappears with weight loss, and a few kilos is already enough, with less sugar, soft drinks and white bread, less alcohol and more exercise. Coffee helps. ALT falls within weeks, and the liver recovers completely.
How do I tell alcohol, muscles and liver apart?
With the values beside it. Alcohol lifts gamma-GT considerably and lets AST rise more than ALT. Muscles give a high AST with an almost normal ALT and a normal gamma-GT, usually after hard training. Fatty liver gives an ALT higher than AST, with high triglycerides, a low HDL and belly fat alongside. And a problem in the bile drainage lets ALP and bilirubin rise more than ALT.
Which medicines and supplements raise ALT?
Paracetamol in high doses, some antibiotics, statins in the first weeks, some drugs against epilepsy and rheumatism, anabolic steroids, and herbal preparations such as green tea extract, kava and some slimming products. If the rise began shortly after something new, that is the first suspect; after stopping, the value usually falls within weeks.
Do I need to fast for an ALT test?
No. ALT barely moves with food. What does count: do not have blood drawn in the days after hard training, because muscles lift ALT and above all AST temporarily, and compare over time at the same lab. The other liver values and your fat metabolism come from the same draw.
Which tests include ALT?
ALT 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): ALT. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): ALT. 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): ALT. 2026. bepalingenwijzer.certe.nl
- 4.Clinical Diagnostics, lab guide (Dutch): ALT. 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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