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Liver

ALT (alanine aminotransferase): what the liver enzyme does and what a raised level means

ALT, in full alanine aminotransferase, is an enzyme: according to the NVKC, the Dutch society of clinical chemists, a protein that helps cells convert one substance into another. ALT is found mainly in the liver, and according to the NVKC smaller amounts are found in the kidneys, the heart and the muscles.

When liver cells are damaged, ALT leaks from the liver into the blood according to the NVKC, and that can happen before there are symptoms. According to the authors of a 2023 study, a low ALT goes together with loss of muscle mass in the general population. Only a blood test shows how much ALT is in the blood.

Star-SHL, Unilabs, Certe and Diagnostiek voor U use an upper limit of 45 U/l for adult men and 34 U/l for adult women.

Doctor's Assessment Included

ALT is an enzyme, a protein that helps cells convert one substance into another; it is found mainly in the liver and enters the blood when liver cells are damaged. The four laboratories use an adult upper limit of 45 U/l for men and 34 U/l for women.

  • According to the NVKC, a slightly raised ALT without symptoms is not given a meaning straight away; only when the value is more than twice the upper limit is a search for the cause advised.
  • A normal or slightly raised ALT does not rule out serious liver disease such as cirrhosis, which is why ALT is often combined with other liver tests.
  • According to Thuisarts, when ALT is only slightly high, there is no clear cause and the person is not really ill, the GP can wait a few weeks and then test the blood again.

Reference Ranges

See the value that applies to you:

Choose male or female — this range differs by sex.

Enter your age — this range changes with age.

This range also depends on context such as cycle phase or sample material; the highlighted rows apply to your group.

Your reference range
u/l
8 71 u/l
Reference ranges by group, in u/l
Male · 1–5 years 9–35 u/l
9 35
Male · 6–12 years 10–35 u/l
10 35
Male · 13–18 years 9–42 u/l
9 42
Male · 19–50 years 13–71 u/l
13 71
Male · 51–65 years 13–64 u/l
13 64
Male · 66–80 years 11–54 u/l
11 54
Male · 81 years and older 9–42 u/l
9 42
Female · 1–5 years 10–33 u/l
10 33
Female · 6–12 years 9–33 u/l
9 33
Female · 13–18 years 8–35 u/l
8 35
Female · 19–50 years 9–44 u/l
9 44
Female · 51–65 years 11–52 u/l
11 52
Female · 66–80 years 10–46 u/l
10 46
Female · 81 years and older 8–37 u/l
8 37
8 71 u/l

Source: NVKC Reference population: Dutch general-practice population (NUMBER, n = 7,574,327)

Reference ranges may vary between laboratories. When you order a test, a BIG-registered doctor assesses your personal results in context. For treatment decisions, discuss your results with your GP.

Check your own value

ALT (Alanine Aminotransferase): what Dutch laboratories use

Reference ranges by group, in u/l
Star-shl · Male 0–45 U/l
0 45
Star-shl · Female 0–34 U/l
0 34
Unilabs · Male · 19 years and older 0–45 U/l
0 45
Unilabs · Female · 19 years and older 0–34 U/l
0 34
Certe · Male · 18 years and older · a limit, not a range < 45 U/L
45
Certe · Female · 18 years and older · a limit, not a range < 34 U/L
34
Diagnostiek voor U · Male · a limit, not a range < 45 U/L
45
Diagnostiek voor U · Female · a limit, not a range < 34 U/L
34
0 49.5 u/l

Source: Star-shl

Source: Unilabs

Source: Certe

Source: Diagnostiek voor U

Each value as the laboratory itself publishes it, retrieved in 2026.

ALT (Alanine Aminotransferase): what this test measures

The ALT test measures the activity of the enzyme ALT in the blood, expressed in units per litre (U/l). According to the NVKC, the result is compared with other liver tests, such as alkaline phosphatase (ALP), gamma-GT and AST, another enzyme found in the liver among other places.

ALT (Alanine Aminotransferase): why this value matters

According to the British liver guideline of the BSG, ALT counts as more liver-specific than AST, because it occurs outside the liver only in low concentrations. According to the BSG, the idea that the height of an abnormal liver test tracks the outcome is not supported by the literature: the diagnosis and the reason for the test determine the course more clearly.

According to the BSG, the most common causes of abnormal liver tests that lead to chronic liver disease, fatty liver, alcohol-related liver disease and hepatitis C, often go together with only a mild or moderate abnormality.

ALT (Alanine Aminotransferase): how the blood test works

Referral
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The draw
A blood draw from a vein in the arm, at a partner laboratory's draw site. No home kit, no finger prick.
Which test
Liver checkup · €89,- · General checkup · €199,-
Where
650+ draw sites run by independent laboratories across the Netherlands. Draw sites

ALT (Alanine Aminotransferase): how to prepare

  1. Better no hard training beforehand

    Recommended

    Hard exercise in the 48 hours before can raise this value temporarily. Plan the draw on a rest day if you can.

  • Water is always fine. Drink as usual beforehand, it makes the draw easier.
  • Take your usual medication, unless your own doctor told you otherwise.

ALT (Alanine Aminotransferase): when is testing worthwhile?

According to the NVKC, an ALT test is requested when a doctor suspects damage to the liver or wants to rule it out. According to the NVKC, ALT is also requested in people who may have been infected with hepatitis B or C, who drink too much alcohol, who have liver disease in the family or who have to take medicines that may damage liver cells.

According to the NVKC, ALT is sometimes tested with mild complaints such as tiredness, to look for a longer-standing liver disease.

ALT (Alanine Aminotransferase): symptoms of a high or low value

Low Levels

A low ALT goes together with loss of muscle mass in the general population, write the authors of a 2023 study in European Urology Open Science. According to Malakouti and colleagues, most chronic alcoholics are deficient in vitamin B6, which is needed to make ALT, and that deficiency lowers the production of ALT more than that of AST. Star-SHL and Unilabs give 0 U/l as the lower limit.

High Levels

According to Thuisarts, a raised ALT can come from a fatty liver, medicines that can damage the liver, alcohol, an inflammation of the liver caused by a virus such as hepatitis B or glandular fever, gallstones or drugs, among other things, and sometimes it does not become clear why the liver tests are abnormal. According to the NVKC, an ALT of more than 15 times the normal value is almost always caused by acute hepatitis, which is usually caused by a virus.

During a liver investigation, Thuisarts advises an appointment with the GP for a yellow skin or yellow whites of the eyes (jaundice), light grey stools, dark urine, pain in the upper right abdomen, a belly that keeps growing, weight loss without a known reason or feeling more and more ill.

ALT (Alanine Aminotransferase): causes of a low or high value

What lowers the value

  • Low muscle mass

    In studies of the general population, a low ALT goes together with loss of muscle mass.

  • Vitamin B6 deficiency

    Vitamin B6 is needed to make ALT; a deficiency, which is common with long-term heavy drinking, reduces how much ALT is made.

What raises the value

  • Fatty liver

    A fatty liver, too much fat in the liver, can raise ALT and the other liver tests in the blood.

  • Alcohol

    Drinking alcohol is one of the causes of a raised ALT and other raised liver tests.

  • Medicines and drugs

    Medicines that can damage the liver, including ones bought without a prescription, and drugs such as cocaine or ecstasy can raise ALT and the other liver tests.

  • Acute viral hepatitis

    An ALT more than 15 times the upper limit is almost always caused by acute hepatitis, which is usually caused by a virus.

  • Heavy weight training

    In one study, ALT stayed raised for at least 7 days after an hour of heavy weight training in healthy men who were not used to it.

ALT (Alanine Aminotransferase): lifestyle and this value

A raised ALT is one to discuss with your GP. According to Thuisarts, the GP can wait a few weeks and then test the blood again, if there is no clear cause, the person is not really ill and the liver tests are only a little too high; other options are extra blood tests for hepatitis A, B or C, an ultrasound of the abdomen or a referral to a gastroenterologist.

With abnormal liver tests, Thuisarts advises stopping alcohol for a while, losing weight if overweight by eating healthily and moving more, and discussing medicines, herbs or vitamins bought in a shop with the GP.

ALT (Alanine Aminotransferase): frequently asked questions

What does a slightly raised ALT mean?

According to the NVKC, a slightly raised ALT without symptoms is not given a meaning straight away. According to the NVKC, only when the value is more than twice the upper limit is a search for the cause advised.

Can ALT be normal in serious liver disease?

Yes, according to the NVKC, in some serious liver diseases, such as cirrhosis, liver cancer and blocked bile ducts, the ALT value can be normal or only slightly raised. That is why, according to the NVKC, ALT is often combined with other liver tests such as ALP and AST.

How long does ALT stay high after acute hepatitis?

According to the NVKC, in acute hepatitis ALT stays strongly raised for 1 to 2 months, and the result is only normal again after 3 to 6 months.

ALT (Alanine Aminotransferase): sources

  1. den Elzen WPJ, Brouwer N, Thelen MH, Le Cessie S, Haagen I-A, Cobbaert CM. NUMBER: standardized reference intervals in the Netherlands using a 'big data' approach. Clin Chem Lab Med 2018;57(1):42-56. (retrieved 2026) doi.org
  2. Star-shl, Labbepalingen (referentiewaarden per bepaling), star-shl.nl, geraadpleegd 2026-10-01 (retrieved 2026) star-shl.nl
  3. Unilabs, Bepalingenklapper (referentiewaarden per bepaling), bepalingenklapper.nl, geraadpleegd 2026-10-01 (retrieved 2026) bepalingenklapper.nl
  4. Certe, Bepalingenwijzer (referentiewaarden per bepaling), bepalingenwijzer.certe.nl, geraadpleegd 2026-10-01 (retrieved 2026) bepalingenwijzer.certe.nl
  5. Diagnostiek voor U, eLabgids (Referentiewaarden DvU), diagnostiek.getincontrol.eu, geraadpleegd 2026-10-01 (retrieved 2026) diagnostiek.getincontrol.eu
  6. Laufer M, et al. Low Alanine Aminotransferase, as a Marker of Sarcopenia and Frailty, Is Associated with Shorter Survival Among Prostate Cancer Patients and Survivors. Eur Urol Open Sci 2023. (retrieved 2026) pmc.ncbi.nlm.nih.gov
  7. Malakouti M, et al. Elevated Liver Enzymes in Asymptomatic Patients - What Should I Do? J Clin Transl Hepatol 2017;5(4):394-403. (retrieved 2026) pmc.ncbi.nlm.nih.gov
  8. NHG, Thuisarts.nl: De levertesten van mijn bloed zijn niet goed, geraadpleegd 2026-10-06 (retrieved 2026) thuisarts.nl
  9. NVKC, Alles over testen: ALAT, allesovertesten.nl, geraadpleegd 2026-10-06 (retrieved 2026) allesovertesten.nl
  10. Pettersson J, et al. Muscular exercise can cause highly pathological liver function tests in healthy men. Br J Clin Pharmacol 2008;65(2):253-259. (retrieved 2026) pmc.ncbi.nlm.nih.gov

Test Products

This marker is included in the following test panels.

General checkup

General checkup

A broad blood test covering 18 values across liver, kidneys, thyroid, heart, vitamins and blood count.

ALT (Alanine Aminotransferase) GGT (Gamma-Glutamyl Transferase) Creatinine eGFR (Estimated Glomerular Filtration Rate) TSH (Thyroid Stimulating Hormone) Total Cholesterol HDL Cholesterol LDL Cholesterol Triglycerides Glucose (Fasting) Vitamin D (25-OH) Vitamin B12 Ferritin Hemoglobin Leukocytes (WBC) Platelets (Thrombocytes) CRP (C-Reactive Protein) MCV (Mean Corpuscular Volume) Cholesterol/HDL Ratio Non-HDL Cholesterol LDL/HDL Ratio
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ALT (Alanine Aminotransferase)

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