Liver enzyme tests
Liver enzymes are proteins that have specific functions. Some of these enzymes leave the liver and enter the blood when the liver is injured.
Several things can cause liver enzyme levels to increase. These include side effects from prescription and over-the-counter medications, herbs, vitamins and supplements, exposure to toxic fumes, high alcohol intake, a new or existing hepatitis infection, and coming off drugs and/or alcohol.
Many HIV drugs can cause liver enzymes to increase—though not usually to dangerous levels. In some cases, those drugs need to be stopped or switched.
People taking HIV drugs (or any other drugs processed by the liver) need to have liver enzyme levels measured with their routine blood tests. This is especially important if they also have HCV. Liver enzymes tests are often called liver function tests (LFTs), although they do not really measure liver function. The results from these tests should be looked at in relation to other information.
ALT and AST
Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are two important liver enzymes.
The liver produces ALT, which helps produce salts and amino acids (which are used to make proteins). Increases in ALT are usually a signal of liver inflammation or damage.
However, ALT is not a good marker for predicting HCV disease progression, or indicating how much your liver may already be damaged. This is because liver enzyme levels regularly go up and down in people with HCV.
Up to a third of people with chronic HCV always have a normal ALT, but some of them will have serious liver damage.
Normal liver enzyme levels, even over time, do not mean that you have no liver damage.
- ALT should be monitored routinely, as if it continues to increase, it may mean HCV is getting worse.
- AST is another enzyme involved in the production of amino acids but because it is made in the heart, intestines, and muscles, it is not a sensitive marker for liver injury. AST is often used to monitor liver inflammation and damage in combination with other tests.
ALP, GGT, bilirubin, albumin and prothrombin time
It is important for people with HCV and HIV/HCV to undergo routine monitoring of ALP, GGT, bilirubin, albumin and prothombin time.
- Alkaline phosphatase (ALP) is another enzyme that is present in tissues throughout the body, including the liver. If blood levels of ALP increase, this can be a sign of disease or damage to tissues. Your doctor can also test specifically for ALP from the liver. Some medications, including the HIV protease inhibitors atazanavir and indinavir, can cause ALP elevations. Elevated ALP from the liver is a sign of blocked bile ducts caused by liver disease.
- Gamma glutamyl transferase (GGT) is enzyme involved in metabolism that is produced in the bile ducts. `Any type of liver disease, heavy drinking, and some medications can increase levels of GGT.
- Bilirubin is a waste-product from the breakdown of red blood cells. The liver is involved with processing bilirubin. When the liver is damaged, it may be unable to process bilirubin, and the total bilirubin levels increase. Jaundice, dark urine and pale stool are common signals of increased bilirubin. Some drugs, including the HIV protease inhibitors atazanavir and indinavir, can cause increased bilirubin levels.
- 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. Abnormally low levels of albumin are a sign of serious liver damage.
- PT (prothrombin time, pro-time) PT testing measures the amount of time it takes for blood to clot. When the liver is damaged, its ability to make clotting factors is impaired. If this time increases – referred to as a ‘prolonged PT interval’ it shows that the liver is not working so well.