Confirmatory Test Used for Detecting HIV Infection

Tests for HIV and AIDS

ELISA, which stands for enzyme-linked immunosorbent assay, is used to detect HIV infection. If an ELISA test is positive, the Western blot test is usually administered to confirm the diagnosis. If an ELISA test is negative, but you think you may have HIV, you should be tested again in one to three months.

ELISA is quite sensitive in chronic HIV infection, but because antibodies aren't produced immediately upon infection, you may test negative during a window of a few weeks to a few months after being infected. Even though your test result may be negative during this window, you may have a high level of the virus and be at risk of transmitting infection.

Types of HIV Tests

There are three types of HIV tests: antibody tests, antigen/antibody tests, and nucleic acid tests (NAT). Antibodies are produced by your immune system when you're exposed to viruses like HIV. Antigens are foreign substances that cause your immune system to activate. If you have HIV, an antigen called p24 is produced even before antibodies develop. HIV tests are typically performed on blood or oral fluid. They may also be performed on urine.

How the Test is Performed

HIV testing can be done by:

• Drawing blood from a vein
• A finger prick blood sample
• An oral fluid swab
• A urine sample

Why the Test is Performed

• Testing for HIV infection is done for many reasons, including for:
• Sexually active individuals
• People who want to be tested
• People in high-risk groups (men who have sex with men, injection drug users and their sexual partners, and commercial sex workers)
• People with certain conditions and infections 
• Pregnant women, to help prevent them from passing the virus to the baby