Hepatitis C | Pathology Tests Explained

Robert Harrod and how pathology diagnosed him with autoimmune hepatitis

Robert Harrod, a retired shift worker, was feeling unusually tired with no reason – “I could have fallen asleep at the drop of a hat.” After several weeks of this he visited his GP.
The results of his blood test indicated his liver wasn’t functioning properly. To find the cause, Robert needed an invasive liver biopsy, where a small sample of his liver was given to the pathology team.

What is being tested?

Hepatitis C is a virus that can infect and damage the liver. In most cases, it is contracted through exposure to blood (usually from sharing contaminated needles while injecting drugs or, before 1990, through a blood transfusion. It can also be passed from mother to baby. Other ways it can occasionally be transmitted include needlestick injuries in a healthcare setting, tattooing, body piercing and rarely through sexual transmission. Hepatitis C antibody is produced in response to exposure to the hepatitis C virus (HCV). The most common test for HCV looks for these antibodies in your blood. Other tests detect the presence of the actual virus, the amount of virus present, or determine the specific subtype of virus.

How is it used?

Each of the six most common tests has a slightly different purpose:

Anti-HCV tests detect the presence of antibodies to the virus, indicating exposure to HCV. These tests cannot tell if you have an active viral infection, only that you were exposed to the virus in the past. Usually, the test is reported as "positive" or "negative". There is some evidence that, if your test is "weakly positive", it may not mean that you have been exposed to the HCV virus. In Australia a positive Anti-HCV test has to be confirmed by a different antibody test. If one test is "positive" or "weakly positive" and the second test is negative, this is termed a "discordant result". A discordant result often means that you have not been exposed to the HCV virus however sometimes this can mean you may have been exposed recently so it is likely that a repeat test will be requested.
HCV RIBA test is an additional test to detect the presence of antibodies to the virus. It can determine if the positive anti-HCV test was due to exposure to HCV or represents a false signal. "Weakly positive" anti-HCV tests can be re-tested with HCV RIBA to see if they are positive or not. Like the anti-HCV test, the RIBA test cannot tell if you are currently infected, only that you have been exposed to the virus.HCV-RNA test identifies whether the virus is in your blood, indicating that you have an active infection with HCV. It is usually performed by a test called a qualitative HCV; the result is reported as a "positive" or virus "detected" if any virus is found; otherwise, the report will be "negative" or "not detected" if no virus is found. The test is also used after treatment to see if the virus has been eliminated from the body. This method is used for early detection and is one of the most sensitive methods for testing.
Viral Load or Quantitative HCV tests measure the number of viral particles in your blood. Viral load tests are often used before treatment to help determine how long treatment needs to be given (along with other factors, such as your age, gender, the changes seen in a liver biopsy, and genotype, discussed below). With newer forms of treatment, it is also used to follow response to treatment by comparing the amount of virus before and after treatment.
HCV Antigen testing is a test much like the RNA test in that it looks for the presence of the virus in the blood although rather than looking for the genetic material of the virus like the RNA test, this test looks for part of the virus called an antigen. While it can be used to help determine if someone is currently infected with Hepatitis C it is not commonly used.
Viral genotyping is used to determine the kind, or genotype, of the virus present; there are currently 6 major types of HCV; the most common (genotype 1) in Australia is less likely to respond to treatment than genotypes 2 or 3 and usually requires longer therapy. Genotyping is often required before treatment is started to give an idea of the likelihood of success and how long treatment may be needed.

When is it requested?

Hepatitis C infection is a common cause of chronic liver disease . About 75-85 per cent of those infected develop chronic hepatitis, and about 20 per cent of those develop cirrhosis. HCV testing is recommended in the following cases:

If you have ever injected illegal drugs
If you received a blood transfusion or organ transplantation before mid-1990*
If you were ever on long-term dialysis
For children born to HCV-positive women
For health care, emergency medicine, and public safety workers after needlesticks, sharps, or mucosal exposure to HCV-positive blood
For people with evidence of chronic liver disease

_{* The blood supply has been monitored in Australia since February 1990, and any units of blood that test positive for HCV are rejected for use. The current risk of HCV infection from transfused blood in Australia is less than 1 case per million transfused units.}

HCV testing is done in a sequential way. First an anti-HCV test is done. A positive anti-HCV test may be confirmed with an HCV RIBA test, especially if the test is "weakly positive" or "discordant". A positive anti-HCV test is usually followed by a Qualitative HCV-RNA test to see if the infection is still present. HCV viral load and genotyping may be done to plan treatment. Viral load and qualitative HCV RNA are also used to monitor response to treatment to see if the virus has been or is being eliminated.

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