Some blood tests are used to determine whether your liver is damaged or inflamed. Although these tests help your doctor evaluate how well your liver is working, they cannot tell if you have hepatitis C.
Tests that assess liver function
Your doctor may do tests to measure certain chemicals produced by the liver. These tests can help your doctor check how well your liver is working. Tests may measure:
Prothrombin time (a measure of blood clotting). It may also be called International Normalized Ratio (INR).
Tests that check for inflammation of the liver (liver enzyme studies)
If you have increased levels of the following, your liver may be damaged:
Alanine aminotransferase (ALT or SGPT)
Aspartate aminotransferase (AST or SGOT)
An increased level of alkaline phosphatase (AP) may indicate blockage of bile ducts.
Why It Is Done
Liver tests are done when a medical history or physical exam suggests that something may be wrong with your liver.
These tests can also help diagnose long-term (chronic) infection. Hepatitis C infection is considered chronic when liver enzymes remain elevated for longer than 6 months.
If you are being treated with antiviral therapy, you may have liver tests from time to time to see whether treatment is working.
Findings of liver function tests may include the following:
All levels are within the normal range.
One or more levels are outside the normal range. Abnormal liver function tests may indicate that your liver is inflamed or is not working normally. This can be a sign that you have a viral infection.
What To Think About
Elevated liver enzymes can be caused by many things other than hepatitis C, such as obesity, hepatitis B, autoimmune hepatitis, certain medicines, or long-term alcohol use. So you will need other tests (such as a hepatitis C antibody blood test or a liver biopsy) to confirm a diagnosis of hepatitis C.
People with chronic hepatitis C have abnormal liver enzyme levels most of the time. But the levels can fluctuate between normal and abnormal throughout the course of the disease.
Liver tests can be used to help you and your doctor develop a treatment plan. Signs that you might need treatment include:
Liver enzyme levels that remain above normal for longer than 6 months, which is evidence of chronic infection.
Detectable levels of hepatitis C virus in your blood (positive hepatitis C RNA test). This is a sign of an active infection.
Evidence of serious liver damage. This is detected with a liver biopsy.