There are many tests for diagnosing HIV.

Some tests search for antibodies that are produced by the immune system, some target antigens that activate the immune system, and others detect HIV’s genetic material. Each test has a different window period, which is the time between potential exposure to the virus and when the test becomes accurate and able to detect the virus. This timeframe also varies depending on each person’s immune system. It is important to note that HIV can be transmitted even during the window period.

HIV antibody test:

• This is a blood test that looks for the antibodies produced by the body in response to an HIV infection. 

• Generally detectable within a few weeks to a few months after infection. 

• The most common HIV antibody test is ELISA, which detects both HIV 1 and 2.

• Generally, antibody tests conducted using blood from a vein are more sensitive in detecting HIV infection at an earlier stage compared to tests performed by a finger prick or oral fluid samples.

Window period: within 23 to 90 days after exposure. Some individuals may take longer to develop detectable antibodies.

Rapid HIV antigen/antibody test (blood or oral fluid):

• Tests that look for antibodies and antigens and provide results in around 20 minutes. 

• Tested through a simple finger prick. 

• Often used in clinics, community health centers, and outreach programs.

• Detects both HIV 1 and 2.

Window period: Similar to HIV antibody blood tests, within a period of 2 to 8 weeks, with some individuals taking longer to develop detectable antibodies.

HIV antigen/antibody test:

• These tests, like the p24 antigen test, look for specific viral proteins, in addition to antibodies.

• They can detect HIV 1 and 2 infections before the body has produced detectable levels of HIV antibodies.

The p24 Antigen test uses the ELISA technique to detect the p24 antigen, a viral protein, in the blood. This test is used for early detection in acute HIV 1 and 2 cases before the production of sufficient and detectable antibodies.

Window period: These tests can detect both HIV antibodies and the p24 antigen, reducing the window period to about 2 to 4 weeks after exposure.

Nucleic acid test (NAT):

NATs, such as PCR (polymerase chain reaction) tests, directly detect the genetic material of HIV 1 and 2. These tests are highly sensitive and mainly detect the viral load that represents the amount of the virus in the blood.

Window period: within 10 to 33 days after exposure. They have the shortest window period among available tests.

CD4 test:

This test is used to measure CD4 T lymphocyte count in the blood. A lower CD4 count suggests a weakened immune system, which can be a sign that HIV has progressed to a more advanced stage. It primarily helps the healthcare provider assess the person’s status and together make informed decisions about the treatment.

Tests| Window period

Antibody test | 23 - 90 days

Rapid antigen/antibody test | 18 - 45 days

Antigen/antibody test | 18 - 45 days

NAT test | 10 - 33 days

The "window period" refers to the time between exposure (unprotected sexual encounter) and the time of accurate testing. The duration of the window period can vary depending on the type of infection and the specific testing methods used.

Written by:

Cristel Lahoud | Sexual health educator, midwife

Cristel Lahoud is a sexual health educator at Marsa, holding a Bachelor's degree in Midwifery and currently pursuing a Master's degree in Clinical Psychology. Her profound dedication lies in raising awareness and promoting advocacy for both sexual and reproductive health.

Written by:

Lena Mhanna | Sexual health educator, nurse

Lena Mhanna, a passionate sexual health educator, with a bachelor's degree in Nursing Science is on a mission to break taboos, provide knowledge and empower individuals to enhance their sexual health and well-being.