Why PCR test is not conclusive?

Why everybody on this forum says that PCR is never conclusive? It is actually looking for the virus, not antibodies. Isn't it supposed to be more precise than ELISA!? If your body is slow to seroconvert, than it means that HIV spreads out quickly and viral load grows, so the PCR is supposed to find the virus more easily. Is my logic wrong?

[alienshadow]

PCR tests are primarily used to measure viral burden in people with confirmed HIV infection, i.e. people who have tested positive for HIV antibody using the ELISA test.

[hopeless4now]

The PCR can give false positives, costs a lot, sometimes gives false negatives and is not easy to perform. You can have an undetectable viral load and test "negative" but still have the virus. This said, an antibody test is much more reliable overall because if you have antibodies they will show...hope this helps.

[worry777]

If it is used to measure the viral burden, then the accuracy of detection is very high, so it can detect extremely small amounts of virus in the blood. Why then not use it for conclusive results? The conclusive timeframe for ELISA is 3 months, but before you seroconvert, the virus spreads quickly in your blood, so you are supposed to have large number of infected cells, so PCR should detect that easily!!?!?! Right!?!?!?

[worry777]

Does anybody know of any FALSE NEGATIVES for PCR?

[Teak]

Just because someone has no detectable VL does not mean that they are not infected.

[worry777]

After reading tons of studies of PCR-RNA tests, it sounds like the main reason FDA does not approve this test is because it gives too many FALSE POSITIVES. Now, insurance companies do not want this test approved because it is more expensive than antibody tests. I did not find even one occurrence of FALSE NEGATIVE. I think, PCR tests should be considered conclusive for NEGATIVE RESULTS (after a certain time, i think it's like 28 days), but NEVER CONCLUSIVE for POSITIVE results, because they do give many FALSE POSITIVES. Any thoughts or arguments on this?

[regularjoey]

No, that is wrong.  You can be negative by PCR and still have HIV.  Teak here will probably test negative on all HIV PCR tests, for example.  That is why a negative PCR is not used to rule out HIV infection.  

[concerned997]

what about DNA PCR, doesnt that detect the virus in your WBCs? Not just the viral load?

[regularjoey]

Doesn't matter, there's still a detection threshold, even if it is very low with some new tests.  The point is that a negative PCR is an excellent indicator that you're negative, but  antibody testing is what is used to rule out HIV infection.  

[pataya6]

So can a low viral load PCR test mean that the person tested is less contagious than someone with a high viral load?