You usually get tested for the hepatitis C virus (HCV) if you’re already seeing a doctor for liver problems or if you may have been exposed through sexual contact or sharing needles with someone with the disease.
Most people with hep C show no symptoms. That's why the CDC recommends that adults born between 1945 and 1965 (Baby Boomers) get a one-time screening. Tests are the only way to know if you have hep C. But the most widely used blood checks for HCV sometimes can miss a very recent infection. Or you may test positive even if the viruses are no longer in your body.
This blood test is the first -- and sometimes the only -- one you may get. Also called the ELISA screen, it checks for chemicals called antibodies that your body releases to fight the virus.
Your screen will be either negative or positive for antibodies. Both results can be faulty.
Negative (nonreactive). This is when your blood shows no signs of HCV antibodies. Most of the time, that’s because you never came in contact with the virus. But sometimes, your negative result can be false, meaning you have HCV. That may happen if you:
- Took the test too soon after your exposure. This test checks for only HCV antibodies, which can take several months to appear.
- Have HIV, a donated organ, or other conditions that weaken your immune system, which can suppress your antibodies
- Get hemodialysis for kidney problems
Positive (reactive). This means you’ve been infected with HCV. But false positives are surprisingly common. More than 1 in 5 people who test positive don’t actually have hepatitis C. Possible reasons include:
- In as many as 1 in 4 people, the HCV goes away without treatment. But even after this “natural clearance,” the HCV antibodies will always be in your blood.
- No test is foolproof. And false positive errors happen more often in groups of people -- like medical workers stuck with tainted needles -- who have low odds of having HCV.
- The test may mistake HCV antibodies for those for lupus, rheumatoid arthritis, and other conditions.
- Babies born to mothers with hep C probably have HCV antibodies. But most newborns aren’t actually infected.
The antibody screen can’t confirm if you have HCV or not. For that, you need a second test that checks for the virus’s genetic material.
After a negative antibody screen, you usually can stop there unless you have reasons to suspect that your result might not be true. Maybe your possible exposure happened very recently. Or you have a medical condition that has dampened your immunity. If so, you should get a more accurate test called an RNA test.
After a positive antibody screen, your doctor almost always will order the RNA test to confirm that you have an infection now.
This measures your “viral load,” the actual amount of HCV in your blood. The RNA test is almost 100% accurate and can detect an infection within a couple of weeks after exposure.
If your RNA test is negative even though you tested positive for antibodies, it means the earlier result was probably not true. For example, you may have had an infection that went away on its own. False negatives with RNA tests are very unlikely, but possible. You could still have super low numbers of the virus in your blood.
If you have HIV or other things that raise your chances for HCV, you might want to get another RNA test later. You can also get a different kind of RNA test, called a “qualitative” test. This checks simply if your blood has any HCV. But it can be more accurate than the viral load test because it can detect even very low amounts of the virus.
If your RNA test is positive, it means you have an active HCV infection. Your doctor will talk to you about treatment. You might get more RNA tests to monitor your disease.
Because RNA tests are so sensitive, false positives can sometimes happen. That’s usually because the sample has been contaminated. Like false negatives, this is very rare.
After a positive RNA test, you’ll get another test to find out which specific strain of HCV you have. It will help your doctor decide on the best treatments for you.