What to know about hepatitis C testing
Hepatitis C (HCV) is an infection that causes scarring in the liver and reduces function in this vital organ. Severe HCV can lead to liver failure. However, early diagnosis can reduce the risk of severe infection.
In this article, we look at how the test works and what the results mean.
What is the HCV RNA PCR test?
The HCV RNA PCR test can help a person find out whether they have HCV.
The HCV RNA PCR test is a blood test. A lab technician looks for the genetic material of the HCV virus, or its ribonucleic acid (RNA). They use a process called a polymerase chain reaction (PCR).
The results of the HCV RNA PCR test help a doctor recommend different ways of reducing the viral load. The viral load indicates how many HCV viral particles are in the blood.
If a doctor suspects that a person has HCV, they will recommend this test early on in the diagnostic process, even if it is not the first test they carry out.
The test can detect the presence of the virus itself, rather than the antibodies that the body creates in response to the virus.
This means that a person does not have to wait until symptoms of the infection develop for a diagnosis.
It can take an average of 6–8 weeks for antibodies to become detectable after an HCV infection begins. However, a doctor can identify the virus itself after about 1-2 weeks by using PCR or another means of direct virus detection.
A doctor will request the test multiple times during a course of treatment for chronic HCV. Repeated testing allows doctors to measure the body's response to a particular method of treatment and make adjustments for the best results.
How it works
Doctors use the HCV RNA PCR in one of two ways:
- a qualitative test determines whether or not the virus is present
- a quantitative test measures the amount of HCV in the bloodstream
There are slight differences in the process for each form of the test.
A doctor may be uncertain whether a person has HCV or not. They can request this test to detect the virus in the bloodstream.
The qualitative test only detects the presence of the virus. It does not determine the number of HCV viral particles in the body.
A doctor will usually recommend an HCV RNA PCR test after a positive HCV antibody test. This test will show if the body is making the antibodies that fight HCV.
While a test that identifies antibodies is usually a good indication of HCV infection, false positives are possible.
A positive test might occur when a person has had a previous HCV infection. This may mean that a person still has antibodies, but the body has already cleared the infection. This happens in about 15–25% of tests.
The virus is more likely to clear in people whose symptoms develop in the early phase of the infection. This is why doctors routinely follow up an HCV antibody test with an HCV RNA PCR test to confirm the diagnosis.
In some cases, doctors may also recommend a third test to confirm the presence of hepatitis C. Doctors call this the transcription-mediated amplification (TMA) test.
The TMA test is not necessary in many cases where an HCV RNA PCR test shows strong enough evidence of an HCV infection.
The results of a quantitative HCV test can help a doctor determine the effectiveness of treatment.
The quantitative HCV RNA PCR test indicates the number of viral copies of HCV in the blood. It works by detecting how much genetic material is present in a small amount of blood.
For many people, the quantitative test has replaced the qualitative test. This is because knowing and understanding the viral load is a crucial step in the treatment process for people with HCV.
The doctor calculates the measurements to match the standard reading, which is the number of international units per milliliter (IU/ml).
Doctors often use a quantitative test when establishing the diagnosis and to monitor the amount of HCV in the bloodstream during treatment. This lets them know how well the body is responding to the treatment, as well as helping them decide on any necessary changes in treatment.
The viral load can vary significantly in the results of the quantitative test.
Doctors usually consider a viral load over 800,000 IU/ml as high. A low viral load would be less than 800,000 IU/ml.
If a quantitative test indicates undetectable viral particle levels, but the qualitative test detects HCV, it means that a person has extremely low levels of HCV in the bloodstream.
Results from the qualitative test
Doctors use the qualitative HCV RNA PCR test to determine whether or not the hepatitis C virus is present in the blood.
If the virus is present, the test will be positive. If the test does not detect the virus, the result will be negative.
If the result is positive, a person will then need a quantitative HCV RNA PCR test. For this reason, many doctors now prefer to skip the first test and use the quantitative test straight away.
Results from the quantitative test
The quantitative test results show how much HCV is in the body. However, whether low or high, the viral load does not reflect levels of damage to the liver.
Other blood tests, ultrasounds, and, rarely, a liver biopsy will help a doctor determine overall liver health.
The vast majority of people achieve SVR and keep HCV at bay for the rest of their lives.
After using an HCV RNA PCR test to confirm the presence of HCV, doctors will work out which strain of the virus is active in the body. This helps a doctor plan the course of treatment.
The primary goal of treatment is to bring down the viral load in the body until it is entirely free of the virus. Doctors know this as a sustained virologic response (SVR).
SVR occurs when the virus is undetectable for 12 weeks or longer after treatment.
Achieving SVR is the best outcome of treatment, as it often means the person is free from hepatitis C, or that treatment has cured hepatitis C.
However, it is essential to remember that once a person achieves SVR, they can still get another HCV infection. They will need to continue making lifestyle changes that help prevent HCV. Changes include stopping the use of intravenous drugs and making sure always to practice sex using a condom or another form of barrier contraception.
A doctor will often refer a person who shows signs of these complications to a specialist for more specific treatment.
HCV RNA PCR tests are an important part of diagnosing and treating HCV. Even after the initial diagnosis, individuals will still require periodic blood tests to make sure treatment is working.
According to the U.S. Department of Veterans Affairs, 99% of people who achieve SVR remain HCV free.
Following a doctor's treatment plan and adhering to regular HCV RNA PCR testing may give people the best chance of SVR and living without chronic HCV.
Is a similar test available for other types of hepatitis?
Yes. When a person has or suspects they have hepatitis B, a doctor will measure their viral load using the HBV DNA PCR test.Cameron White, MD, MPH Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.