Liver enzyme tests and others


Liver enzyme tests: ALT and AST

Liver enzymes are proteins with specific functions (and difficult long names).

If the liver becomes damaged, some of these enzymes leave the liver and enter the blood.

Many things can cause liver enzyme levels to increase. These include:

  • Prescription and over-the-counter medicines.
  • Herbs, vitamins and supplements.
  • Toxic fumes.
  • High alcohol intake or coming off drugs and/or alcohol.
  • New or existing hepatitis infection.

HIV drugs can cause liver enzymes to increase, though usually not to dangerous levels. In some cases, these drugs need to be stopped or switched.

People taking HIV drugs (or other drugs processed by the liver) need to have liver enzymes routinely measured with other blood tests. This is especially important with HCV coinfection.

Raised liver enzymes do not always mean there is liver damage. But persistently high levels can be a sign of ongoing damage that needs to be treated.


Two important enzymes are ALT (alanine aminotransferase) and AST (aspartate aminotransferase).

ALT is produced in the liver and Increases are usually a sign of liver inflammation or damage. However, ALT is not a good marker of either liver damage or changes in liver health. This is because HCV itself causes levels to go up and down.

Up to a third of people with chronic HCV always have a normal ALT, even with serious liver damage.

If an increase in ALT continues to rise, or is getting worse, it may mean continued HCV related inflammation which may eventually lead to scarring (fibrosis).

AST is an enzyme that is made in the heart, intestines, and muscles. AST is only used to monitor liver inflammation and damage in combination with other tests.

  • Normal liver enzymes, even over time, do not mean there is no liver damage.
  • Raised liver enzymes do not always mean there is liver damage, but if they are persistently high this can be a sign of ongoing damage, and that treatment may be a good idea.

ALP, GGT, bilirubin, albumin and prothrombin time

Routine monitoring in coinfection also includes ALP, GGT, bilirubin, albumin and prothombin time (PT).

ALP (alkaline phosphatase) is an enzyme that is present throughout the body, including the liver. If blood levels of ALP increase, this can be a sign of tissue disease or damage. Your doctor can also test specifically for ALP from the liver. Some medications, including the HIV protease inhibitor atazanavir, can increase ALP. Elevated ALP from the liver is a sign of blocked bile ducts caused by liver disease.

GGT (gamma glutamyl transferase) is an enzyme involved in metabolism that is produced in the bile ducts. Any liver disease, heavy drinking, and some medications can all increase GGT.

Bilirubin is a waste product from the breakdown of red blood cells. Before it passes through the liver, where it is mixed with sugars to become water-soluble, it is called indirect or unconjugated bilirubin. Once it has been processed through the liver it is called direct or conjugated bilirubin.

A damaged liver may be unable to process bilirubin, causing an increase in the total bilirubin levels. Usually, a laboratory will subtract the amount of direct bilirubin from the total amount of bilirubin in the bloodstream; the leftover is indirect bilirubin.

Jaundice is an increased level of bilirubin and common signs include a yellowing of the skin and eyes, dark urine or pale stools. Some drugs, including the HIV protease inhibitor atazanavir, and HCV protease inhibitors, can increase bilirubin.

Albumin is a protein made by the liver. It carries drugs, hormones and waste products through the blood and maintains fluid levels within the body. An abnormally low level of albumin is a sign of serious liver damage.

Last updated: 17 August 2017.