what blood tests will tell me the most?

Posted by rachel on June 16, 1999 at 20:00:03
Thank you so much for this forum...As I am requesting my own tests from my PC physician, I need a clarification based on my research so far. What is the difference between the HCV RNA test (which gives a "copies per 1,000") and the PCR RNA (which, it sounds like, is a positive/negative result)?
I have gotten the RNA quantitative results(< 1000), and all normal enzyme levels, but wonder if this PCR is a definitive test that may help me in determining if I really can be considered as "having Hepatitis C". Thanks again for being there for us!

Posted by hfhsm.d.-d.m. on June 27, 1999 at 15:57:37

Dear Rachel:
I really appreciate your questions and the opportunity to talk about PCR tests for hepatitis C RNA..  I am a little confused by your question but I think you are asking about the difference between a qualitative and a quantitative HCV RNA or PCR test and what it means to have a quantitative RNA test "<1000".  These are excellent questions.
First, let me start by reiterating a point that I make frequently but cannot make frequently enough.  The hepatitis C antibody test typically means that someone has been exposed to hepatitis C, but it is the HCV RNA test that confirms an active infection.  Again, 10 to 15% of patients exposed to hepatitis C will clear the infection on their own.  They will often have a positive antibody test but the HCV RNA test or PCR test will be negative.  
Now for your specific questions.  First of all both HCV RNA and the PCR RNA tests are essentially the same test.  Almost all tests for HCV RNA levels use PCR technology.  For a long time there was a test called the bDNA test that was offered by the Chiron company.  It gave HCV RNA levels using non-PCR technology but it is not used as often anymore.
There are two general types of PCR tests for HCV RNA, a qualitative test and a quantitative test.  The quantitative test has the advantage that it uses a modification of the standard PCR assay that can actually give levels of the viral RNA that is present. The disadvantage to this test is that the sensitivity only goes down to between 2000 to 1000 copies/ml of viral RNA depending on which lab is doing the assay.  As a result, if someone gets a result that is "<1000", this typically means the assay did not find any virus.  In someone not being treated, this is usually because no virus is present and the individual is not infected.  However, I cannot entirely rule out that someone has a low level of virus that is between 0 to 1000 copies per/ml.  However, this is fairly unusual.  
The qualitative test has a sensitivity that is typically in the range of 100 copies/ml.  It is usually reported as positive or negative.  A negative test typically means that someone does not have any detectable virus but again there is always a chance that virus is present but that it is below 100 copies/ml.  
The actual amount of virus present is useful information to physicians and to patients and that's why we often prefer the quantitative test.  However, the level of virus is not critical information and some physicians prefer the extra sensitivity of the qualitative test.  
I hope this information is helpful to you.  Good luck. If you have any additional questions or concerns, you can post them through MEDHELP.  The direct number to our liver clinic at Henry Ford is: [phone].  At Henry Ford, we have a very active group of hepatologists with a strong interest in the care and research of hepatitis C.
This response is being provided for general informational purposes only and should not be considered medical advice or consultation.  Always check with your personal physician when you have a question physician when you have a question pertaining to your health.
Posted by rachel on June 28, 1999 at 16:29:08
Thank you so much for responding. You very nicely clarified the difference between the tests and I am now reassured that I do not need another blood test.
This forum has been a great gift. Thank you to all who contribute to it!

Posted by hfhsm.d.-d.m. on July 03, 1999 at 16:21:58

Your  welcome.