Liver Function Test (LFT)
This is a blood test that is used to detect abnormal levels of specific enzyme production in the liver. When the liver is attacked by the hepatitis C virus it becomes inflamed and, as a consequence, some liver cells die and release enzymes. These enzymes are often very specific to certain viruses or conditions.
One of the signs that infection with the hepatitis C virus is resulting in inflammation of the liver is a raised level of ALT (alanine aminotransferase) in the blood. For people who are hepatitis C positive, ALT is the most commonly monitored enzyme in liver function tests. A positive result on an antibody test and elevated ALT levels on a liver function test provide a fairly good indication that an individual is still infected with the hepatitis C virus.
In a Melbourne study several years ago it was found that over 90% of patients with abnormal ALT and positive antibodies had the hepatitis C virus (HCV) detected in their blood using PCR. On the other hand, a positive result for an antibody test combined with normal ALT levels over a period of six months, might mean that the body has cleared the virus and only the hepatitis C antibodies remain. A person with these results may consider having a PCR test. However, in the study, over 50% of people with a positive result on an antibody test and normal ALT levels were found to have HCV detected in their blood.
Liver specialists and general practise doctors often use differences in liver function test results over time (in combination with physical symptoms or other signs of liver disease) to evaluate the progression of hepatitis C in their patients. Unfortunately, these tests do not give a good guide to liver disease progression for an individual patient. For most people an annual liver function test is adequate after consulting a liver specialist.
It is important to remember that ALT levels can fluctuate markedly over even short periods of time and can be affected by other factors, such as stress, some medications, alcohol consumption and diet. In addition, while elevated ALT levels are a measure of inflammation of the liver, there is no clear correlation between high ALT levels and the degree of liver damage. For example, if liver damage has progressed to the point of cirrhosis, liver function tests may show normal ALT levels (other substances also detected by a liver function test may show abnormal levels if this is the case). Due to differences in technology, ‘normal ranges' quoted by laboratories may differ. This means ALT results from one laboratory should not be directly compared with results from another laboratory.
Source - Impact booklet, produced by Hepatitis C Victoria, June 2008