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GENOME INSTITUTE OF SINGAPORE
Genotyping
If you do test positive for hepatitis C, your doctor or the specialist to whom you've been referred will probably order a genotyping blood test. The hepatitis C virus has at least six distinct forms, or genotypes (labeled 1 through 6). In the United States, about 70% of patients have HCV genotype 1. In other parts of the world, other genotypes are more common. Genotype 1 is associated with a poorer response to treatment. Genotyping can help your doctor determine the appropriate hepatitis C treatment and how long treatment should be given.
HCV RNA Tests
Unlike antibody tests, HCV RNA tests directly measure for the presence of the hepatitis C virus. HCV RNA tests may be qualitative or quantitative. Qualitative HCV RNA tests are used to diagnose hepatitis C. Your doctor might choose to perform an HCV RNA test instead of the ELISA, especially if you are at high-risk for hepatitis C. The HCV RNA test will be positive in as little as 1 to 2 weeks after exposure. A positive HCV RNA test means a person has hepatitis C infection. Quantitative HCV RNA tests allow your doctor to determine exactly how much virus is in the blood. This is referred to as the viral load. The viral load is usually expressed as units per milliliter or copies per milliliter. In patients with chronic hepatitis C infection, viral loads vary widely from 50,000 to 5 million copies per milliliter. A higher viral load may not necessarily be a sign of more severe or more advanced disease but it does correlate with likelihood to respond to treatment. HCV RNA tests can also be used to monitor response to hepatitis C treatment. For example, if the viral load decreases during treatment, this suggests that treatment is working and should be continued. Conversely, if the viral load remains the same, it suggests that the patient is not responding to treatment.
Diagnostic Blood Tests
There are specific tests your doctor can do to identify hepatitis C. Blood banks also screen donated blood for hepatitis C and notify you if you have tested positive. Tests for hepatitis C can show if you are infected with the virus or if you were infected in the past.
If you think you are at risk for hepatitis C and want to get tested, ask your doctor for a hepatitis C blood test. Remember, routine blood tests do not test for hepatitis C. The only way you can get tested is to ask specifically for the test.
There are two main types of blood tests that can be used to diagnose hepatitis C:
Antibody tests - Antibody tests detect the presence of antibodies to the hepatitis C virus (e.g, the ELISA and RIBA) tests
HCV RNA tests - These tests specifically detect the presence of the hepatitis C virus particles. HCV RNA can be detected using several methods. The most common method is reverse transcription-polymerase chain reaction or RT-PCR.
Antibody Tests: The ELISA and RIBA
ELISA
The most commonly used initial blood test for hepatitis C is the enzyme-linked immunosorbent assay (ELISA). The ELISA is also sometimes referred to as the EIA. The ELISA tests for the presence of antibodies to the hepatitis C virus. An antibody is a type of immune protein molecule that is produced when bacteria or viruses enter the body. A specific antibody is manufactured against each invader.
In most cases if your ELISA test is negative, it means that you do not have antibodies to the hepatitis C virus and you do not need to be tested further. Although false-negative tests are very rare with the ELISA, they may sometimes occur in patients whose immune systems do not produce enough antibodies, such as people on hemodialysis and people with immune disorders (eg, HIV positive persons).
If you have a high-risk for acquiring hepatitis C (for example, if you have injected drugs, had a transfusion before 1992, etc.) and your ELISA test is negative, your doctor may want to screen you again after a few months. Sometimes antibody tests such as the ELISA might not become positive for 3 to 6 months after a person is infected.
If the ELISA is positive, this generally means that there are antibodies against HCV in your blood; however, it does not necessarily mean that you have hepatitis C. It may be that you were infected in the past and have already cleared the infection. If the ELISA test is positive, your doctor or the specialist will probably perform an HCV RNA test to determine whether there is still virus in your blood or whether you have cleared the infection. In very rare cases, the ELISA may give a false-positive result, such as in people with autoimmune disorders. Again, these can be results can be confirmed with an HCV RNA test.
RIBA
The recombinant immunoblot assay (RIBA) is another test that detects the presence of antibodies to hepatitis C virus in the blood. The RIBA can be used to confirm a positive ELISA, for example, in a blood donor who does not appear to have risk factors for hepatitis C. Blood banks also use the RIBA to test donated blood, especially to confirm blood samples that are HCV-positive by the ELISA.
ALT Tests
The ALT test is a blood test that measures levels of alanine aminotransferase (ALT), a liver enzyme that is produced in higher amounts when the liver is inflamed. High ALT levels can be a sign of hepatitis C, but other conditions can also cause an increase in ALTs, including heart attacks, high triglyceride levels, and other forms of hepatitis.
On the other hand, many people with hepatitis C have fluctuating or normal ALT levels, so a normal ALT test does not necessarily mean that hepatitis C infection can be ruled out.
ALTs are measured in routine blood tests so if your annual blood work results indicate high ALT levels, this may alert your doctor to do further tests to find out the cause.
A higher than normal ALT level does not necessarily mean more serious disease.
Liver Biopsy
Another common test used to classify hepatitis C is the liver biopsy, in which a small piece of liver is removed and examined under a microscope. Many doctors do a liver biopsy whenever a patient has a high alanine aminotransferase (ALT) level (which suggests that the liver is inflamed) to help them confirm what exactly is causing this problem and how serious it is. A liver biopsy can help your doctor or specialist determine how much damage has been done to the liver.
When the liver is damaged (for example, by the hepatitis C virus), it tries to repair itself and forms small scars. This scar formation is called fibrosis. A greater amount of fibrosis indicates more severe and more advanced disease. Based on the results of the liver biopsy, you and your doctor will be able to make more informed decisions regarding treatment. For example, if you are found to have normal or only slightly higher than normal ALT levels and little or no fibrosis on liver biopsy, your doctor may decide to postpone treatment because this type of chronic hepatitis C has little chance of progressing to cirrhosis. On the other hand, if the degree of fibrosis is moderate to severe, your doctor may decide to begin treatment immediately.
Liver biopsy is done in the hospital and requires local anesthesia. For more information on liver biopsy and what to expect before, during, and after the procedure, visit http://www.niddk.nih.gov/health/digest/pubs/liverbiopsy/liverbiopsy.htm.
Your doctor has other tests available, too. Don't be afraid to ask what tests he or she has done, what other tests are available, and what the tests may tell you about your condition.