AST (aspartate aminotransferase)

AST (aspartate aminotransferase) is an enzyme found in the liver, but also in the heart, skeletal muscles, kidneys and red blood cells. It is most often measured alongside ALT and GGT as part of liver testing, and high AST signals liver or muscle damage. A doctor assesses the more likely source from its relationship with other results.

Who the test is for

• people having general or preventive check-ups, alongside ALT and GGT;
• people with symptoms suggesting liver disease: fatigue, nausea, discomfort under the right rib cage, yellowing of the skin and eyes or dark urine;
• people at risk of fatty liver, those who regularly drink alcohol and those taking medicines that may burden the liver;
• people with known liver disease, for monitoring;
• people with suspected muscle damage, alongside CK.

What AST indicates

When cells containing AST are damaged, the enzyme enters the blood. Because it occurs in several organs, AST is less liver-specific than ALT. It is therefore almost always interpreted alongside ALT and GGT, and when a muscle source is suspected, also with CK (creatine kinase).

AST was once used to diagnose heart attacks, but this is now outdated: heart attack diagnosis uses an ECG and troponin in emergency care. Chest pain, difficulty breathing or cold sweats require emergency medical help rather than waiting for laboratory results.

Save with a panel

Test AST (aspartate 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 AST (aspartate aminotransferase) (21) ›

Preparation and sample

Blood is taken from a vein. Fasting is not essential for AST, but if glucose or lipids are measured from the same sample, arrive fasting. Avoid alcohol for at least a day beforehand and very strenuous exercise for several days beforehand because muscle AST can temporarily rise. State which medicines, supplements and herbal preparations you take. If a sample is damaged during collection and red blood cells break down (haemolysis), their AST falsely raises the result and testing is repeated.

What high AST 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; values in young children are physiologically slightly higher than in adults. Mildly elevated AST is common and most often does not indicate serious disease, but a doctor considers the degree of elevation, its relationship to ALT and whether it persists.

Most common causes

• Fatty liver: in metabolic dysfunction-associated steatotic liver disease (MASLD), AST is mildly elevated and usually lower than ALT.
• Alcohol: AST is often higher than ALT, sometimes twice as high, and GGT is elevated.
• Medicines and supplements: for example high doses of paracetamol, some antibiotics and tuberculosis medicines, statins and herbal preparations.
• Viral hepatitis and infectious mononucleosis: AST and ALT can rise severalfold in acute hepatitis and usually moderately in mononucleosis. Hepatitis B and C are checked using hepatitis markers.
• Cirrhosis: in advanced liver disease, AST is often higher than ALT, although both may be only mildly elevated.
• Muscles: strenuous exercise, muscle injury or inflammation; CK is also elevated while GGT is normal.
• Other causes: increased red blood cell breakdown (haemolysis), thyroid disease and coeliac disease.

The AST/ALT ratio

The AST-to-ALT ratio helps guide investigation. In fatty liver and viral hepatitis it is usually below 1, meaning ALT is higher. A ratio above 2 with elevated GGT suggests alcohol-related liver damage, while a ratio above 1 can also occur in cirrhosis of any cause. The ratio is only a guide and does not establish a diagnosis alone.

What follows an elevated result

With mild elevation, 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, 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). Values several times above the upper limit, particularly with jaundice, severe abdominal pain, fever or confusion, require prompt medical assessment.

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. AST is most often measured as part of the Liver Health Panel, together with ALT and GGT.

Frequently asked questions

Can exercise raise AST?

Yes, and this is a common cause of mildly elevated AST in young, active people. Strenuous weight training, prolonged running or competition can raise it for several days. CK is usually also elevated while GGT is normal. Repeat testing after approximately a week without strenuous exercise.

What does high AST with normal ALT mean?

The source is most often outside the liver: muscles after exertion or injury, sample haemolysis or increased red blood cell breakdown. Alcohol may also be involved. A doctor usually repeats testing and requests CK, GGT and a blood count.

Is high AST a sign of heart disease?

Rarely as an isolated finding. AST rises after a heart attack but is no longer used to diagnose it. High AST without symptoms is much more often due to liver or muscle conditions. Chest pain always requires urgent assessment, regardless of results.

What is a normal AST level?

The limit depends on the laboratory, method, sex and age, so always use the reference interval printed on the report. Men generally have slightly higher values than women.