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A laboratory can analyze a biological sample for traces of human immunodeficiency virus (HIV) using a HIV PCR test. The PCR stands for polymerase chain reaction, the technique that the lab analyst uses to identify any trace of the virus. Someone who wishes to undergo a HIV PCR test typically visits a medical professional, who takes a sample, or he or she can opt to take a sample at home and mail it to the laboratory.
Once a person has become infected with HIV, though such possible transmission methods as unprotected sexual intercourse, shared needles or contaminated blood transfusions, the virus multiplies. A HIV PCR test can pinpoint viral particles in people that have been exposed as recently as two weeks before the test. This is in contrast to cheaper tests such as antibody tests, which may require months of infective growth to give a positive result.
Blood is the primary sample for a HIV PCR test. In many developed countries, blood donations undergo screening in this manner. Newborn babies of mothers with HIV also require a HIV PCR test instead of one of the other test options, as the babies retain maternal anti-HIV antibodies for a time after birth. An adult who wishes to opt for this test often needs to visit a clinic or doctor's office, where the doctor draws vials of blood for the test. Another alternative may be to use a home-sampling kit, where someone can place blood from a finger prick onto a sample card, and then mail it to the testing laboratory.
When the laboratory receives the sample, it places some of the blood in a centrifuge machine, and this machine spins the sample at high speed. The speed splits the sample of blood cells into layers, depending on size and weight. Then an analyst can remove the layer of specific blood cells he or she wishes to test for viral particles.
The analyst adds chemicals to the cells to break them down and release the genetic material inside. This genetic material may include the HIV virus, as it lives and replicates inside the host cells. He or she then adds the genetic material to a mixture of substances.
These substances can recognize a portion of the genetic material of the virus, cut out this portion of the material, and copy the pieces over and over. Generally, these substances also inadvertently recognize other parts of the virus genetic strand too, and so makes lots of different sized pieces, of which only one is the portion of interest. A piece of equipment called a PCR machine provides a warm place for these substances to work in, which helps speed up the replication of the pieces.
After the PCR machine finishes its cycle, the analyst removes the sample. He or she then runs it through an agarose gel under an electric current. This separates the pieces of genetic material into lengths. The analyst knows how long the identifying portion of the virus's genetic material is, compared to other potential lengths, allowing for detection of the virus in the original blood sample.