Human immunodeficiency virus (HIV) is diagnosed using one of three types of tests: nucleic acid, antigen/antibody, and antibody tests. These tests may use either a sample of your blood or saliva to get results. A healthcare provider can also use a urine sample. No test can detect the virus immediately after exposure. The window period for detection depends on the type of test and ranges from 10 to 90 days.

HIV attacks white blood cells, also called CD4 cells, in the immune system. These cells help your body fight infections. HIV destroys CD4 cells, weakening your immune system and leaving you vulnerable to other illnesses.

Getting tested is the only way to diagnose HIV. Without treatment, HIV can damage the immune system and progress to acquired immunodeficiency syndrome (AIDS). Knowing your HIV status allows you to begin treatment sooner, reduce symptoms, and stabilize the spread of HIV in your immune system.

You can get tested at a healthcare provider’s office, family planning clinic, pharmacy, mobile testing van, or during HIV/AIDS awareness events. At-home HIV tests are also available at some pharmacies and clinics. These locations can also connect you with specialists who provide HIV care, treatment guidance, and social support services.

Who Should Get Tested For HIV

Experts recommend HIV testing as part of routine healthcare, including for pregnant individuals. The Centers for Disease Control and Prevention (CDC) advises that everyone aged 13–64 get tested for HIV at least once. Testing is especially important if you have symptoms of acute or chronic HIV.

Not everyone experiences symptoms, and early signs can resemble the flu. Healthcare providers recommend testing at least once a year for people at higher risk.

High-risk behaviors include:

  • Being a man who has sex with men

  • Having multiple sexual partners

  • Having sex with someone who is HIV positive

  • Having unprotected vaginal or anal sex

  • Being diagnosed with another STI, hepatitis, or tuberculosis

  • Sharing needles, syringes, or injection equipment

If you think you have been exposed to HIV, talk to your doctor about post-exposure prophylaxis (PEP). PEP is an emergency HIV medication taken within three days of possible exposure. It is not for regular use and should only be taken in urgent situations.

Types Of HIV Tests

HIV carries an antigen called protein 24 (p24). Antigens are foreign substances that trigger your immune system to respond. In reaction, your body produces antibodies to fight the virus.

Healthcare providers use three types of tests: antibody tests, antigen/antibody tests, and nucleic acid tests (NAT). The p24 antigen appears earlier than antibodies, making some tests more effective at early detection. Providers may use more than one test to confirm a diagnosis.

Antibody Test
This test checks for HIV antibodies using blood, saliva, or urine. Most rapid and at-home self-tests are antibody tests. They can detect HIV antibodies 23–90 days after exposure. Results are usually available within 30 minutes for rapid tests.

Antigen/Antibody Test
This test checks for both HIV antigens and antibodies. A blood sample is taken from a vein and sent to a lab. It can detect HIV 18–45 days after exposure.

There are also rapid antigen/antibody tests done with a finger stick. These tests have a longer detection window (18–90 days) but provide results in less than 30 minutes.

Nucleic Acid Test (NAT)
This test looks for the actual virus in the blood. A sample is taken from a vein and analyzed in a lab. NAT can detect HIV 10–33 days after exposure and measure viral load (how much virus is in the blood). This test is especially useful for people with symptoms of acute HIV who test negative on other tests.

Stages Of HIV

HIV progresses through three stages:

  • Acute HIV stage: Begins two to four weeks after infection. Most people experience flu-like symptoms.

  • Clinical latency (chronic HIV) stage: Starts as soon as one month after exposure and may last 10–15 years. Some people have no symptoms, but the virus continues to multiply at low levels.

  • AIDS stage: Without treatment, HIV weakens the immune system severely. Symptoms include rapid weight loss, pneumonia, and swollen lymph nodes. At this stage, people are at high risk for serious infections and cancers.

Diagnostic Criteria For AIDS

A person is diagnosed with AIDS if:

  • Their CD4 cell count falls below 200 cells per cubic millimeter of blood.

  • They develop one or more AIDS-defining illnesses (such as lymphoma, herpes, or cervical cancer), regardless of CD4 count.

A Quick Review

HIV is a chronic condition that attacks CD4 cells in the immune system, weakening the body’s defenses against infections. There is no cure, but an early diagnosis is key to starting treatment.

Testing is the only way to know your HIV status. Antibody, antigen/antibody, and nucleic acid tests can confirm infection. Results vary depending on the test type and when exposure occurred.

An HIV diagnosis may feel overwhelming, but healthcare providers can help you begin treatment and manage your condition. With proper care, many people live long, healthy lives with HIV.