HlV tests are used to detect the presence of the HlV in the human body. By detecting HlV antibody, antigens or RNA, people can be diagnosed whether they are infected with the virus or not. Blood test is the most common HlV test to detect HlV infection.
How soon can I have a test after sex?
After being infected with HlV, it takes a period of time for antibodies/ antigen/ virus to reach a detectable level. This period is known as the “window period”. The length of window period varies among individuals and various laboratory tests. Some may take up to three months. With the advancement in testing technology, not only has the window period of antigen and antibody tests been shortened, HlV can now be detected through RNA test. As RNA test is done by checking the genetic substance of HlV, its window period is shorter than antigen and antibody tests. Thus, HlV can be detected through blood test at an earlier stage of infection.
- HlV p24 antigen test: P24 antigen is one of the proteins that make up of the HlV. After HlV infection and before the production of antibodies, the level of p24 antigen will elevate in the body. This can be detected in the blood sooner than HlV antibodies.
- HlV antibody test: When HlV enters the body, the body reacts in response to fight the infection and the immune system starts to produce antibodies. Although these antibodies cannot fight off the infection, their presence can help diagnose whether a person has HlV inside the body.
- HlV antigen & antibody combo test: Using the “fourth-generation” technology, the combo test can detect both HlV p24 antigen and HlV type 1 & type 2 antibodies. It is generally recommended to have the HlV combo test 21 days after sex.
- HlV RNA test: RNA test looks for genetic substance of the HlV with blood sample to detect the very early infection when HlV antibodies are undetectable. It is generally recommended to have the HlV RNA test 7 days after sex.
What does the test results mean?
The virus/ antigen or antibody level varies from one to another. If doing a test within the window period, there is a chance of having a “false negative” result given the level of virus/ antigen or antibody is still undetectable. Therefore, if you have engaged in unprotected sex or other high-risk activity, there is still the risk of HlV infection and you may still infect others with HlV. It is recommended to re-test 3 months after the suspected infection day to confirm the result.