Aspartate aminotransferase (AST) Test

You don’t need any special preparation for an AST test. The test uses a simple blood sample taken from a vein in your arm.

What the test measures 

AST is an enzyme found mainly in your liver and heart, with smaller amounts in muscle. When cells in these organs are injured, they release AST into your bloodstream. 

AST is usually measured alongside other liver enzymes like ALT (alanine transaminase) and ALP (alkaline phosphatase). Comparing these results helps your doctor determine which type of liver disease you might have. 

What your results mean 

If your AST is very high 

Very high AST levels, more than 10 times the upper limit of normal, usually indicate acute hepatitis. This is rapidly developing liver inflammation, often caused by viruses or toxic substances like paracetamol overdose. 

In acute viral hepatitis, AST usually stays elevated for about 1 to 2 months. However, it can take as long as 3 to 6 months to return to normal. 

If your AST is moderately high 

Moderately high levels, often less than 4 times the upper limit of normal, are seen in several conditions. These include chronic hepatitis, alcohol-related liver disease, blockages in bile ducts, fatty liver disease, autoimmune liver disease and cirrhosis. 

AST can also increase when red blood cells break down (haemolysis) or from heart, kidney, or muscle damage. Your doctor will consider your other test results and symptoms to identify the cause. 

In chronic hepatitis and alcohol-related liver disease, AST often varies between normal and slightly increased. Your doctor may request regular testing to determine the pattern of change. 

If your AST is slightly high or normal 

In some liver diseases, AST may be only slightly elevated or close to normal. This can happen with partial bile duct blockages, fatty liver disease, autoimmune liver disease, cirrhosis, and certain liver cancers. 

A high AST to ALT ratio may help predict long-term complications like cirrhosis in people with chronic viral hepatitis, chronic alcoholism or non-alcoholic fatty liver disease. 

Important considerations 

Although AST is found in heart and other muscles, another enzyme called creatine kinase (CK) is present in much higher amounts. Doctors usually use CK rather than AST to detect heart or muscle injury. 

Strenuous exercise or injections into muscle tissue can temporarily raise your AST levels. Some medicines can also damage the liver or muscle, increasing AST. This includes both prescription medicines and some herbal health products.

If your AST is high, your doctor will work with you to identify the cause. This usually involves other blood tests and possibly imaging scans like ultrasound or CT scans of your liver. 

Treatment depends on the cause of your elevated AST. This might include antiviral medicines for hepatitis, stopping alcohol if you have alcohol-related liver disease, or changing medicines that may be damaging to your liver. 

Your doctor will monitor your AST levels over time to check how well treatment is working. In some cases, you may need referral to a liver specialist for further investigation and management.

Several factors can raise your AST levels: 

• strenuous exercise or recent injury 
• injections into muscle tissue 
• medicines that can damage the liver or muscle 
• herbal supplements or health products 
• breakdown of red blood cells (haemolysis) 

Tell your doctor about all medicines, supplements, and herbal products you’re taking. Also mention any recent strenuous exercise or injuries before having the test. 

AST is usually measured as part of a liver function test panel alongside other enzymes and markers. 

Common tests done with AST include: 

• ALT (alanine transaminase) – another liver enzyme 
• ALP (alkaline phosphatase) – helps identify bile duct problems 
• GGT (gamma-glutamyl transferase) – another liver enzyme 
• Bilirubin – a yellow pigment removed by the liver 
• Albumin – a protein made by the liver 
• Hepatitis virus tests – if viral hepatitis is suspected 
• Antibody tests to check for autoimmune liver disease 
• Tests for rarer inherited disorders that can affect the liver e.g. Caeruloplasmin, Copper, Ferritin, Iron, Alpha‑1 antitrypsin 

Your doctor may also request imaging scans like ultrasound or fibroscan to assess your liver structure and check for scarring (fibrosis or cirrhosis). 

Liver disease can be caused by many things, including viral infections, excessive alcohol, obesity, and certain medicines. Early liver disease often has no symptoms, which is why blood tests are important for detection. 

For more information about liver disease, symptoms, causes, and treatment, visit the British Liver Trust website and NHS liver disease information.