ALT (alanine aminotransferase)

ALT (alanine aminotransferase) is an enzyme found mainly in liver cells. When they are damaged or inflamed, ALT enters the blood, making an elevated value one of the most sensitive signs of liver strain. The test does not show the cause, so results are interpreted alongside other liver tests, symptoms and your medicines.

Who the test is for

• adults having general or preventive check-ups, most often alongside AST and GGT;
• people who are overweight or have type 2 diabetes, high blood lipids or metabolic syndrome, because of the risk of fatty liver;
• people who regularly drink alcohol;
• people taking medicines that may burden the liver, when a doctor recommends monitoring;
• people with fatigue, nausea, discomfort under the right rib cage, yellowing of the skin and eyes or dark urine;
• people with chronic hepatitis and other liver diseases, for monitoring.

What ALT indicates

ALT is also found in the kidneys, heart and skeletal muscles, but in much smaller amounts than in the liver. It is therefore more liver-specific than AST, which is abundant in muscles and the heart. A doctor most often considers them together with GGT, because their relationship helps narrow down possible causes.

ALT indicates liver cell damage rather than how well the liver functions. Normal ALT therefore does not exclude all liver disease: values can be normal or only mildly elevated in fatty liver and even advanced cirrhosis.

Save with a panel

Test ALT (alanine aminotransferase) is also included in these panels.

Liver health panelAST, ALT, GGTPrice of individual tests: 9.60€9.00€Details ›Extended liver health panelAST, ALT, AP, GGT, total bilirubin, total protein17.00€Details ›General preventive panelCBC, glucose, cholesterol, HDL and LDL cholesterol, triglycerides and 430.00€Details ›

All panels including ALT (alanine aminotransferase) (21) ›

Preparation and sample

Blood is taken from a vein. Fasting is not essential for ALT, but if glucose, lipids or PT are measured from the same sample, come in the morning after fasting. Avoid alcohol for at least a day beforehand and very strenuous exercise, particularly weight training, for several days beforehand, because it can temporarily raise ALT. At sampling, state which medicines, supplements and herbal preparations you take.

What high ALT means

Results are expressed in units per litre (U/L). The reference interval depends on the method, sex and age and is printed on the report; men generally have slightly higher values than women. Mildly elevated ALT is common and most often does not indicate serious disease, but should not be ignored, particularly if it remains high on repeat testing.

Most common causes

• Fatty liver: metabolic dysfunction-associated steatotic liver disease (MASLD, formerly non-alcoholic fatty liver disease) is the most common cause of mildly elevated ALT. ALT is usually higher than AST, and GGT is often mildly elevated.
• Alcohol: in alcohol-related liver damage, AST is usually higher than ALT and GGT is elevated.
• Medicines and supplements: for example high doses of paracetamol, some antibiotics, epilepsy medicines, statins, anabolic steroids and herbal preparations.
• Viral hepatitis: acute hepatitis can markedly raise ALT, while chronic hepatitis B and C may cause no symptoms for years. It is checked using hepatitis markers. ALT also rises in infectious mononucleosis.
• Muscles: strenuous exercise or muscle injury can raise ALT, but CK (creatine kinase)and AST are usually even more elevated.
• Less common causes: autoimmune hepatitis, excess iron accumulation (haemochromatosis), Wilson’s disease, coeliac disease and thyroid disease.

Values several times above the upper limit suggest acute liver damage, for example from viruses, medicines or toxins, and require prompt medical assessment. If high ALT accompanies yellowing of the skin and eyes, severe abdominal pain, fever or confusion, see a doctor immediately.

What follows an elevated result

With mild elevation and no symptoms, a doctor usually repeats testing after several weeks while advising avoidance of alcohol and strenuous exercise. If elevation persists, further blood tests and liver ultrasound follow (we performabdominal ultrasound only in Split), with gastroenterology referral if needed. In fatty liver, a doctor can calculate the FIB-4 index from AST, ALT, age and platelet count to help assess the risk of liver scarring (fibrosis).

Low ALT

Low ALT generally has no clinical significance. Very low levels are sometimes seen with vitamin B6 deficiency, as the enzyme needs it to work.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed on the Contact page). Prices for all tests and panels are available in the service price list. ALT is most often measured as part of the Liver Health Panel, together with AST and GGT.

Frequently asked questions

What is a normal ALT level?

The limit depends on the laboratory, method, sex and age, so always use the reference interval printed on the report. A value near the upper limit in someone who is overweight or has diabetes is still worth showing to a doctor.

Can ALT be high after exercise?

Yes. Strenuous weight training or prolonged running can temporarily raise ALT because it is also found in muscles, while AST and CK usually rise even more. After intense exercise, repeat testing after approximately a week without strenuous training.

What does it mean when ALT is higher than AST?

This is the most common pattern in fatty liver and viral hepatitis. When AST is markedly higher than ALT, a doctor considers alcohol, advanced liver disease or a muscular source. The ratio is only a guide and is interpreted alongside other results.

How can high ALT be lowered?

It depends on the cause, which must first be established. In fatty liver, gradual weight loss, regular physical activity and limiting alcohol help. Do not stop medicines yourself; show the results to your doctor. “Liver cleansing” products have no proven benefit, and some may themselves burden the liver.