What’s the difference between PCR and a confirmatory test?
Sep 14, 2008
AN HIV confirmatory test is done when a person’s blood shows he or she is HIV-positive using a screening test. HIV screening tests are very sensitive, but not very specific for HIV.
Face HIV with Dr Watiti
Dear Doctor,
What is the difference between an HIV confirmatory test and a PCR test?
Mary
Dear Mary,
AN HIV confirmatory test is done when a person’s blood shows he or she is HIV-positive using a screening test. HIV screening tests are very sensitive, but not very specific for HIV.
Screening tests can give false positive results, which must be confirmed, through a confirmatory test, which is not very sensitive, but specific for HIV.
If both the screening test and confirmatory test are positive, then the person is reported as being HIV-positive. If the two tests disagree, then another test known as a tiebreaker is used to decide the final result.
PCR stands for Polymerase Chain Reaction, which is a test done to detect antigens of HIV as opposed to the above-mentioned three tests, which look for antibodies formed against HIV in the body of someone infected by the virus.
These antibodies take time to form and they may not be detected in the body until after six weeks to three months following the infection.
This is the so-called window period. So to diagnose HIV during this period, we use the PCR method.
PCR is also used to diagnose HIV infection in children born to HIV-positive mothers before they reach 18 months, because if the antibody tests are used during this period, they may detect maternal antibodies that are still in circulation in the blood of the baby at this time.
Dear Doctor,
What is the difference between an HIV confirmatory test and a PCR test?
Mary
Dear Mary,
AN HIV confirmatory test is done when a person’s blood shows he or she is HIV-positive using a screening test. HIV screening tests are very sensitive, but not very specific for HIV.
Screening tests can give false positive results, which must be confirmed, through a confirmatory test, which is not very sensitive, but specific for HIV.
If both the screening test and confirmatory test are positive, then the person is reported as being HIV-positive. If the two tests disagree, then another test known as a tiebreaker is used to decide the final result.
PCR stands for Polymerase Chain Reaction, which is a test done to detect antigens of HIV as opposed to the above-mentioned three tests, which look for antibodies formed against HIV in the body of someone infected by the virus.
These antibodies take time to form and they may not be detected in the body until after six weeks to three months following the infection.
This is the so-called window period. So to diagnose HIV during this period, we use the PCR method.
PCR is also used to diagnose HIV infection in children born to HIV-positive mothers before they reach 18 months, because if the antibody tests are used during this period, they may detect maternal antibodies that are still in circulation in the blood of the baby at this time.