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Hepatitis C: How Testing Works
A hepatitis C investigation is complicated. Public health disease investigators go beyond looking at antibody and RNA (ribonucleic acid) test results to understand how disease may be circulating in an outbreak situation.
Test results alone may not tell the full story about whether someone had an infection at some point in their life and whether they posed an exposure risk to others. Public health disease investigators are specially trained to look at all test results, notes from medical staff, and information from the people themselves. We use science and experience to put these clues together to create a more complete picture.
In our Investigating Hepatitis C post May 4, we talked about the detective work we do and the testing that occurs to identify an infection. In this post, we’ll take a closer look at what testing does and does not tell us, and how it helps us with disease investigations.
Last time, we talked about the two types of tests we use to diagnose hepatitis C: the antibody test and the viral test. Most people will only need a hepatitis C antibody test. If this test is negative, that usually tells us that you have never been exposed to hepatitis C and don’t have an infection. But if you were exposed to the virus within the previous six months, you will need to get retested six months after the last exposure. That’s because it can take up to six months after exposure for the body to produce antibodies that would show up in the test results.
Testing tells only part of the hepatitis C story
If your hepatitis C antibody test result is positive, that means you were exposed to the virus and infected at some point in your life. But the antibody test won’t tell us if you still have the virus. A viral test—called an RNA test—tells us if you have the virus in your blood. If you do, an RNA test can tell us how much virus is there. This test is very sensitive and can detect very low levels of the virus.
If the RNA test is positive, that means that you currently have hepatitis C and can spread it. The virus spreads through the blood of someone who has a hepatitis C infection. The good news is new treatments are available that will cure more than 90% of people infected.
About 15%-25% of people will fight off the virus without any treatment. Their antibody test will always be positive, but their RNA test will be negative. This means you don’t have the virus in your blood and can’t spread the disease to anyone else. But if you were exposed to hepatitis C at some point in the future, you could get infected again.
Tests provide only a snapshot of your blood at the time of testing. They will not tell us how long you have had the disease or when you were first infected. So, even though you might have a negative RNA now, when first infected your RNA would have been positive.
When test results are neither positive nor negative
Sometimes the hepatitis C antibody test is reported as equivocal. That simply means the result is neither positive nor negative. In this case, the test needs to be done again with a new specimen. In very rare circumstances, the test results will not be what we expect. Consider this example:
- Someone with a negative antibody test should also have a negative RNA. So, if we receive test results with a negative antibody and a positive RNA, we know we need to dig deeper. You may need to have additional testing, or you might have a brand new infection. No one test will tell us if this is a new infection. We must use as many pieces of information—as many clues—as we have available to us to determine what’s happening. Other test results as well as any symptoms you had at the time of the testing—are also other clues.
Through our increased investigations, we expect to identify more people in our community with hepatitis C and connect them with treatment.
Have a question about hepatitis C? Ask us in the comment section, and we’ll answer you in a future blog post. Learn more about the virus, symptoms, and risk factors.