What Factors Affect the Accuracy of a PCR HIV Test?

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  • Written By: Erin J. Hill
  • Edited By: Bronwyn Harris
  • Last Modified Date: 20 September 2016
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The polymerase chain reaction (PCR) test used to detect human immunodeficiency virus (HIV) is typically considered to be very accurate, although there are several factors that come into play. The test is highly sophisticated and must be read by healthcare professionals who are well trained in deciphering the results. In most cases, the PCR test is not used for routine HIV testing except for in infants who are born to an HIV-positive mother.

There are several types of HIV test and each one has its own level of accuracy. Rapid response tests are typically considered the least accurate, while antibody tests and PCR tests are the most accurate. Antibody tests are the most commonly used because they are extremely reliable when used at least three months after potential exposure. The accuracy of a PCR HIV test is not fully understood, but they are considered fairly accurate for use under certain circumstances.

When considering how accurate a PCR HIV test might be, several factors play a role. The first involves the skills of the laboratory staff reading the test. PCR tests use advanced screening methods to pick up on the genetic material of HIV rather than antibodies. It is not an easy test to read and decipher, so many false results may be caused by human error. Only those who are fully trained and experienced in reading and performing the test should do so when testing for HIV.


Another variable is the length of time between when a person is exposed to the virus and testing. While both the PCR and antibody tests can usually detect traceable levels of the virus within a few weeks after exposure, both tests are most accurate at three months past exposure. No matter which type is used, a follow-up test is always performed to ensure that results are as accurate as possible.

Use of the PCR test for HIV is not done on a routine basis in most situations because it is difficult and expensive to administer. Many labs do not have the right equipment to perform these tests. The PCR test may be used in newborns born to an HIV-positive mother since antibodies from the mother's bloodstream can continue to show up in the infant's blood tests for several months after birth even if he or she is HIV-negative. This makes the accuracy of the test more reliable in these cases.


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Post 6

I was exposed to the HIV infection one month back with an Asian sex worker. We did not have sex, but did have contact. I know most of the people will say it's a negligible risk, but I believe it's an exposure.

I went later on and had these tests: an Antibodies test three days later was negative (I know it was in vain).

An Antibodies test (eclia) 10 days after exposure was negative (0.07).

An HIV 1-2 abs+p24 AG (CMIA) 21 days after exposure was non reactive (0.08 s/co).

An Hiv1-2 PCR RNA 21 days after exposure said nothing was detected.

Now, 43 days after exposure I have had a slight fever, with some bumps on my hands and

my back. I have also had a headache and my skin has been burning and I am scared/

Were all this tests at less than 21 days pointless? If I were infected, would it be shown on one of these tests? Some people say the PCR-RNA test is not reliable and not approved by the CDC. Is that true? Do you suggest I have more testing?

Post 4

I had my elisa test and it is negative, but the pcr rna is reactive. Does this mean that I am HIV positive?

Post 3

@anamur, @burcinc-- I think we need to differentiate between the PCR DNA test and PCR RNA test. The PCR DNA test is the one which is used to test infants for HIV as well as adults. This test is actually really sensitive and can pick up even small amounts of the virus, so it is very effective in diagnosis and should ideally be used 2-4 weeks after potential infection. The reason is that after 4 weeks, if the person is infected with HIV, the body will produce antibodies at which point an antibody test can be done. Considering the expense and equipment required to do a PCR DNA test, it's not necessary if an antibody test can be done instead.

There is also a PCR RNA test which is not used to diagnose HIV but rather to follow the disease after a confirmed infection. The PCR RNA is approved by the FDA. The PCR DNA is not unapproved. It's just not approved as a stand-alone HIV test. So it should be followed by another test like the antibody test to confirm the results.

The time period in which the test is done can cause an inaccurate result.

Post 2

@anamur-- As far as I know, the PCR test is accurate around 95% of the time when the test is done within one month of exposure. I think the exceptions may occur when the test is done so soon that the HIV virus is still very few in the body and it is not detected. But I think 20 days is enough time for the virus to multiply to an amount that can easily be detected by the test.

So your friend's test is probably accurate. If she's concerned she can also have an antibody test done for confirmation.

A flu shot shouldn't affect the accuracy of the test. The test is looking for the genetic makeup of the HIV virus, not any other virus.

Like the article said, I doubt that anyone would get inaccurate results with PCR unless there is human error in the analysis.

Post 1

My friend got the PCR HIV test about 20 days after the potential exposure and tested negative. What are the chances that the test gave wrong results because it was too soon?

What's the rate of success with this HIV test before the 3 month period after exposure?

My friend heard that HIV tests might not always be accurate and she's afraid that that's what happened in her case. She also got a flu shot a few days before the HIV test. Could that have changed the results at all?

I'm trying to learn more about the PCR test so that she is relieved of her worries or goes for another test later if she needs to. I read yesterday that PCR has not been approved by the FDA yet. This is also something that worries me. Why would the FDA not approve something that has high accuracy?

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