Medical News Today: HCV RNA PCR test: Qualitative and quantitative results

The HCV RNA PCR test is a blood test that helps doctors diagnose hepatitis C. The test is used to measure the level of the hepatitis C virus in the bloodstream.

In this article, we look at how the test works and what the results mean.

What is the HCV RNA PCR test?

Person having blood sample taken for testing by gloved nurse.
The HCV RNA PCR is a blood test used to diagnose HCV and measure the level of HCV in the blood.

The HCV RNA PCR test is a blood test that looks for the genetic material of the hepatitis C virus, also called its RNA, and uses a process called a polymerase chain reaction (PCR).

Its name comes from the abbreviations for what it tests for and the process used:

  • HCV — hepatitis C virus
  • RNA — ribonucleic acid
  • PCR — polymerase chain reaction

A doctor may recommend different ways of reducing the amount of virus in the body, otherwise known as the viral load, depending on the results of the HCV RNA PCR test.

HCV RNA PCR tests are often given early on, as they can detect the virus itself rather than antibodies to it that the body creates. This means people do not have to wait until their body begins to fight the infection to be diagnosed.

While it can take an average of 6 to 8 weeks after a hepatitis C infection for antibodies to be detected, it may only take 1 week to detect the virus directly by using PCR or other means of direct virus detection.

The test is also checked multiple times during treatments for chronic hepatitis C. This repetition allows doctors to measure any response the body is having to a particular method of treatment.


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How it works

The HCV RNA PCR test is used in one of two ways. It is either qualitative, meaning it determines whether or not the virus is present, or it is quantitative, meaning it measures the amount of HCV in the blood stream.

These two forms of the test are carried out slightly differently.

Qualitative

Blood sample being transferred for testing in lab by technician.
The qualitative test detects the virus, but unlike the quantitative test, it does not measure the level of HCV in the blood.

In cases where doctors are uncertain if someone has hepatitis C or not, an HCV RNA PCR test can be used early on to detect the virus in the bloodstream.

The qualitative test only detects if the virus is present or not. It does not determine how much of the virus is present.

An HCV RNA PCR test will usually be given after a hepatitis C antibody test. A hepatitis C antibody test will show if the body is making the antibodies that fight hepatitis C.

While this is usually a good indication that the person is infected with the hepatitis C virus, false positives are possible.

A positive test can also occur when a person has been infected with hepatitis C in the past, so the antibodies are present, but the body has cleared the infection. This happens in about 15–25 percent of cases.

The virus is even more likely to clear in those people who develop symptoms in the early phase of the infection. This is why doctors routinely follow up a hepatitis C antibody test with a HCV RNA PCR test to confirm their diagnosis.

In some cases, doctors may also recommend a third test to confirm the presence of hepatitis C. This is called the transcription-mediated amplification test, or simply TMA test.

The TMA test is not necessary in many cases where an HCV RNA PCR test shows strong enough evidence that the body is infected with hepatitis C.

Quantitative

The quantitative HCV RNA PCR test is used to get a reading of the amount of HCV in the blood at any given time.

In most cases, 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.

The viral load is the amount of actual viral particles in the bloodstream. The HCV RNA PCR test finds this number by detecting how much genetic material is present in a small amount of blood.

The measurements are calculated to match the standard reading, which is the number of international units per liter, written as IU/L.

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 determine if any changes in treatment are needed.

Viral load

The viral load that is measured using the quantitative test can vary greatly, reaching numbers as high as 100,000,000 million IU/L and as low as less than 15 IU/L.

A high viral load is usually considered over 800,000 IU/L, whereas a low viral load is considered anything under 800,000 IU/L. Some doctors consider 400,000 IU/L to be the cut-off for a low viral load.

Results from the qualitative test

The qualitative HCV RNA PCR test will be used to determine whether or not the hepatitis C virus is in a person’s blood.

If the virus is present, the test will be positive. If the virus is not detected by the test, 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 prefer to skip the first test and use the quantitative test straight away.


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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 that have been caused by an infection. Other blood tests, ultrasounds, and a liver biopsy are more helpful in determining overall liver health.

Next steps

Doctor speaking to male patient on bed
Once HCV has been diagnosed, the strain will need to be identified to create a treatment plan.

After using an HCV RNA PCR test to confirm that HCV is present, doctors will work to identify the strain of HCV involved. This helps guide the treatment plan.

The primary goal of treatment is to lower the viral load in the body until the virus has been removed completely. This is known as a sustained virologic response or SVR.

SVR occurs when the virus is no longer detected in a person for 12 weeks or more after treatment.

Achieving SVR is the best outcome of treatment, as it often means the person is considered to be free from hepatitis C, or that hepatitis C is in remission.

However, it is important to remember that once SVR is achieved, reinfection is still possible. Lifestyle changes that help prevent the spread of hepatitis C infection need to be continued.

Doctors will also combine treatments with other tests that monitor for conditions that include cirrhosis, enlarged blood vessels, and liver cancer, which are all associated with hepatitis C.

Anyone with signs of these disorders will often be referred to a specialist for more specific treatment.


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Outlook

HCV RNA PCR tests are an important part of diagnosing and treating hepatitis C. Even after the initial diagnosis, periodic blood tests will still be necessary to check the effectiveness of someone’s treatment.

According to the U.S. Department of Veterans Affairs, 99 percent of people who achieve SVR remain free of the virus for the rest of their lives.

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 hepatitis C.

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