Antibody tests

Antibodies are produced by your immune system when you are exposed to viruses like HIV.  However, these antibodies are not protective in nature.

An HIV antibody test detects the presence of such antibodies. A positive test result shows that a person has been infected. A negative HIV antibody test result after the window period means that a person has not been infected. Nowadays we can have HIV antibody test with blood, oral fluid (oral mucosal transudate; it is not the same as spitting out saliva) or urine.

Antigen/antibody tests

Antigens are foreign substances that cause your immune system to activate. If you have HIV, an antigen called p24 (a protein component of the HIV viral core) is produced even before antibodies develop.

An antigen/antibody test looks for both HIV antibodies and antigens. This is also known as combo test or fourth generation test. An antigen/antibody test has a shorter window period than an antibody test, which means that an infection can be detected earlier.

Nucleic acid test

A nucleic acid test detects the genetic material of virus in the blood. While a nucleic acid test can detect HIV sooner than other types of tests, the main use of nucleic acid test is to measure the viral load (HIV viral load test) for monitoring the treatment effectiveness.