What's the difference between PCR RNA and PCR DNA and when would one use one rather than the other? Also, is it preferable to use plasma or serum to conduct the tests or does it matter? Thanks...
Response from Dr. Holodniy
RNA PCR is usually used to measure HIV RNA in "cell free" plasma or serum, referred to as viral load. The assay converts the viral RNA to DNA which gets amplified millions of times in order to be detected and quantified. It can also be used to measure HIV RNA inside cells. This measures how many copies the virus is making of itself in the cell. It is not routinely used in clinical practice. DNA PCR measures the amount of naturally converted HIV viral RNA to viral DNA that gets incorporated into the chromosomes of someones cells. It is useful as a sensitive test for diagnosis. It is not very useful as a marker for disease progression or to monitor therapy. Plasma in general yields higher copy numbers than a serum sample. It is important to use the same material when testing serial samples to rule out sample variability. MH
Neither is appropriate for DIAGNOSING HIV infection, except:
1) When a patient presents with symptoms indicative of ARS/PHI and doctors want to diagnose a recent infection (before seroconversion, usually 1-3 weeks post exposure).
2) When a patient is severely immuno-compromised, e.g., undergoing aggressive chemotherapy for cancer or taking high dose anti-rejection drugs for organ transplant.
Many members here like to use these tests to get a so-called "better" or more definitive result that they are HIV-. This is an erroneous use of the tests. Others favor PCR testing to get reassurances that they are HIV negative during the window period.
In your case, however, 6-7 weeks post exposure, PCR is pointless. Your negative ELISA result at 6-7 weeks (from your other post) is highly indicative that you are HIV- (>95%). All you need in one other ELISA/EIA or rapid HIV test at 3 months (12-13 weeks) to remove any remaining doubt.
Both Dr HHH and Dr Bob from thebody.com concur that PCR, in general, should not be used for diagnostic purposes.
thanks, that is what I am praying for. I just don't understand why you feel that PCR tests are bad. I had flue like symptoms. I have oral thrush. Isn't that one of the HIV markers. Belive me if I had no symptoms I wouldn't have bothered testing. And I think that for many people in the same situation as me PCR test is a good option. But yes do take it with another test. I agree on that.... more info below...
Viral Detection: Other methods to establish HIV infection include techniques to detect HIV antigen, DNA, or RNA (Table 2-1). HIV-1 DNA PCR is the most sensitive and can detect 1-10 copies of HIV proviral DNA. None of these tests is considered superior to routine serology in terms of accuracy, but some may be useful in patients with confusing serologic test results, when there is a need to clarify indeterminate test results, for virologic monitoring in therapeutic trials, and for HIV detection when routine serologic tests are likely to be misleading such as in patients with agammaglobulinemia, acute retroviral infection, neonatal HIV infection, and patients in the window following viral exposure. In most cases, confirmation of positive serology is accomplished simply by repeat serology. The sensitivity of tests for detection of HIV varies with the stage of disease and test technique, but is usually reported at >99% for DNA-PCR, 90% to 95% for quantitative HIV-RNA, 95% to 100% for viral culture of peripheral blood mononuclear cells (PBMC), and 8% to 32% for p24 antigen detection.
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