During this time, they take a blood sample to check whether it contains human antibodies (disease-fighting proteins) specific to HIV. The two key types of HIV antibody tests are the enzyme-linked immunosorbent assay (ELISA) and the Western blot.
Also, there is another procedure called “point of care test kits” which tests a sample of saliva taken from the mouth or a spot of blood taken from piercing a finger with a needle.
If the HIV virus has been found, the test result is "positive". The blood is re-tested several times before a positive result is given to the patient. After infection with HIV, it can take three weeks to three months for the virus to show up in the tests. Re- testing may be necessary.
Ultra-sensitive HIV sensor:
Scientists from the Imperial College London, reported in Nature Nanotechnology (October 2012 issue) that they have developed an extremely sensitive sensor that detects viral infections, including HIV. This is a more effective way of detecting an HIV.
Screening for HIV in pregnancy:
All pregnant women are supposed to take up a blood test to check if they have HIV as a part of routine antenatal screening. If untreated, HIV can be passed on from a pregnant woman to her baby during pregnancy, birth or breastfeeding. Treatment in pregnancy greatly reduces the risk of passing on HIV to the baby.