Liver enzymes (ALT and AST): what they mean and what to do

Liver enzymes, also called transaminases or aminotransferases, are enzymes found inside liver cells. When those cells are injured, the enzymes leak into the blood and their level rises. That is why, on a blood test, high transaminases are above all a marker of liver cell damage, and they are elevated almost by definition in hepatitis.

If your test came back with elevated liver enzymes, the first thing is not to panic. It is a very common finding, mild in most cases, and rarely an emergency. The right step is to calmly look for the cause with your doctor, because the number alone does not make the diagnosis.

What are ALT and AST?

Two transaminases are measured in routine blood tests:

• ALT (alanine aminotransferase), formerly called SGPT. It is found mainly in the liver, so it is the more specific marker of liver damage.
• AST (aspartate aminotransferase), formerly called SGOT. It is also present in muscle and heart, so it can rise from causes outside the liver.

This difference matters. A high AST with a normal ALT does not always mean a liver problem: it can reflect intense exercise, a muscle injury, a muscle disease or, less often, a heart problem. ALT, on the other hand, points more clearly to the liver.

Why do they rise?

Liver enzymes rise when liver cells (hepatocytes) are stressed or die and release their contents into the blood. Inflammation of the liver is the most common cause, but they can also rise from a lack of blood supply (ischemia), from certain medications, or from causes outside the liver.

The most common causes of high liver enzymes are:

• Fatty liver disease, now called metabolic dysfunction-associated steatotic liver disease (MASLD). It is the number one cause.
• Alcohol and alcohol-related liver disease.
• Chronic hepatitis B and hepatitis C.
• Medications and supplements, including some over-the-counter products and herbal remedies.
• Less common causes: hemochromatosis, autoimmune hepatitis, celiac disease, thyroid disorders and muscle diseases.

What are the normal values?

The normal range varies by laboratory, but in general a normal ALT is below about 35 IU/L in men and 25 IU/L in women, with slightly different figures at each center. What matters is not only whether the value is “above normal,” but by how much it exceeds it and whether it stays elevated over time. A single, mildly high result is usually repeated before any in-depth workup.

Useful patterns: how high they go and in what ratio

The degree of elevation and the ratio between AST and ALT help point to the cause:

• Mild elevations (up to 3 times the normal value): the most common, suggesting fatty liver or chronic hepatitis from virus B or C, among many other causes.
• Moderate elevations (3 to 10 times): can be seen in viral hepatitis or alcohol-related disease.
• Marked elevations (more than 10 times): suggest acute viral hepatitis, drug-induced injury or ischemia. Very high figures, above 2,000 IU/L, are seen almost only in liver ischemia, acetaminophen poisoning or acute hepatitis.

The ratio between the two enzymes is also informative:

• ALT higher than AST is the typical pattern of fatty liver and chronic viral hepatitis.
• AST higher than ALT, especially a ratio above 2, is characteristic of alcohol-related liver disease. This same ratio tends to reverse when any liver disease progresses toward cirrhosis.

My liver enzymes are high, what should I do?

Do not panic. Elevated liver enzymes are rarely an emergency, and the cause is often treatable or even reversible. Reasonable steps are:

• Repeat the test to confirm it and see the true size of the elevation.
• Review habits and medications: alcohol use, weight, drugs, supplements and herbal products from recent months.
• Look for the common causes with blood tests for hepatitis B and hepatitis C, a metabolic panel and, when appropriate, a liver ultrasound.
• Rule out causes outside the liver when AST is the one mainly raised, such as intense exercise or a muscle problem.

Your doctor will interpret these results together with the rest of your liver tests, such as alkaline phosphatase, GGT and bilirubin, to reach a diagnosis.

See also

• Fatty liver disease (MASLD)
• GGT (gamma-glutamyl transferase)
• Alkaline phosphatase
• Bilirubin