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Hepatitis C PCR


Polymerase chain reaction (PCR) is a technique which is used to amplify the number of copies of  RNA viral particles and, unlike hepatitis C antibody tests that look for the body response to the virus, a PCR (polymerase chain reaction) test looks for actual presence of the virus.

 

There are 3 types of PCR tests

  1. HCV PCR/RNA — looks for the virus, sometimes called 'qualitative test';
  2. HCV PCR viral load — looks for the virus and estimates how many HCV viruses per mL of blood, sometimes called 'quantitative test';
  3. HCV PCR genotype — looks for the virus, and determines the particular type/s of HCV.


PCR testing may be of benefit in cases of needle-stick and other sharps injury in healthcare settings or for exposure-prone sexual practices.  When an individual is found to be positive for antibodies to HCV during blood donation or a health  screening of at-risk populations, detection of HCV by RNA/PCR confirms chronic HCV infection. Despite improvements in the sensitivity of PCR technology, it’s important to assess HCV viral status on the basis of a minimum of 2 PCR tests — over a 6-month period — rather than on the basis of a single PCR test result. This is because it is possible for levels of hepatitis C virus in the bloodstream to fluctuate such that the level of virus may fall so low that the PCR test won’t pick it up. Thus, someone who tests PCR negative may still be infectious.

If you are interested in the science behind PCR testing this link: http://www.scq.ubc.ca/polymerase-chain-reaction/ may be of interest to you

HCV RNA is detectable in serum within one to two weeks when accidental parenteral exposure results in infection. Detection of HCV RNA without antibodies for HCV is strongly indicative of acute hepatitis C; this will be confirmed by subsequent seroconversion. Acute hepatitis C is unlikely if both markers are absent.
Even if people with HCV know their PCR status they should still avoid all blood-to-blood contact. In any situation involving potential blood-to-blood contact, it’s important for everyone to assume that they, and all others, are potentially infectious. If an HCV antibody positive person finds out they are PCR negative, they’d be making a big mistake in sharing any drug injecting equipment, snorting straws, razor blades or razors, tattooing equipment, toothbrushes or other equipment that could transfer blood.
When HCV RNA is undetectable on at least two occasions 6 months apart, it is difficult to distinguish patients who still harbour antibodies after spontaneously resolving HCV infection in the past from patients with false-positive reactivity.
Acute HCV infection is also unlikely if anti-HCV antibodies are present and HCV RNA absent; such cases generally correspond to patients whose liver disorders are due to another cause and who encountered and cleared HCV at some time in the past. These subjects should nonetheless be retested for HCV RNA a few weeks later, as HCV RNA may disappear transiently before chronic replication becomes detectable.
Finally, when both anti-HCV antibodies and HCV RNA are detected, it is difficult to distinguish acute hepatitis C from an acute exacerbation of chronic hepatitis C, and from acute hepatitis of another cause in a patient who also has chronic hepatitis C.
The diagnosis of acute infection should be based on HCV RNA testing with a sensitive technique. This can be done at any time starting one week after exposure. Antiviral treatment is not urgent in this setting, and can be initiated when symptoms or an increase in serum aminotransferase activity occurs.

Results

What does a positive Hep C Antibody result mean?

If your antibody blood test (the initial test) comes back with a positive result, it is an indicator that you have been exposed to the hepatitis C virus (HCV). However, it does not necessarily mean you have the virus itself. This test looks for your bodies response to hepatitis C, not the actual virus.'

If the antibody test does come back positive, another test called a Hepatitis C PCR (Polymerase Chain Reaction) should be completed to determine the presence or absence of the virus. If HCV is detected by PCR, then this will confirm a viral infection. Your doctor should now refer you to a specialist for assessment.  

If the Hep C antibody test comes back negative, then another Hep C antibody test should be done in 3 months to confirm this result. Hepatitis C has an incubation period of up to 3 months. This means that  it can take up to 3 months after exposure for HCV antibodies to be detected.

If the test was being carried out because of recent high risk of exposure, like a needle stick incident for example, then a Hepatitis C PCR will be a better indicator of HCV infection. The PCR test can be carried out a week after exposure.
If an antibody result comes back negative and PCR is positive identifying the presence of HCV, then this will confirm an acute infection

Polymerase chain reaction (PCR) is a laboratory technique used to amplify the genetic material of a virus to a level that can be detected. The presence or absence of the virus can then be determined. There are 3 PCR tests for the hepatitis C virus (HCV):

  1. Hepatitis C PCR/RNA: Test that looks for the actual virus. Sometimes referred to as a HCV qualitative PCR.
  2. Hepatitis C Viral Load: Also known as an HCV quantitative PCR. Tests for the amount of virus in the blood. The result is given in the number of viral particles per mL of blood.
  3. Hepatitis C genotype: This test determines the genotype of the virus. There are 6 genotypes (1-6) and 21 subtypes of hepatitis C. In New Zealand, the most common types are 1a, 1b, 2a, 2c and 3a.

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