When a person contracts the human immunodeficiency virus (HIV), timing can affect HIV test results. Although tests have become more accurate, none of them can detect an HIV infection immediately after it’s contracted.

The body’s defense mechanisms kick into action after contracting HIV. The immune system begins to develop antibodies to attack the virus. This production of HIV antibodies is called seroconversion. Before seroconversion, there may not be detectable levels of HIV antibodies in a person’s blood.

Before seroconversion, an HIV blood test could produce a false negative result. A positive HIV antibody test will not appear until the body makes enough HIV antibodies to be detected.

The timeframe between when a person contracts HIV and when tests can detect the infection is known as the window period. Everyone’s immune system is different. This makes it difficult to predict how long this stage will last.

Scientists have developed sensitive blood tests since the early days of the HIV epidemic. It’s now possible to detect HIV antibodies, as well as other components of HIV, earlier than ever before. According to the Johns Hopkins Bloomberg School of Public Health, most people test positive within a few weeks of contracting HIV. For others, it may take up to 12 weeks.

During the window period, a person may develop symptoms similar to the flu or other common viruses that include:

  • swollen lymph nodes
  • headache
  • rash
  • fever

Symptoms may last from a few days to a few weeks. And they may range from mild to severe. But it’s possible to pass through the early infection stage without experiencing any symptoms at all. During this time, a person may not even realize that they’ve contracted HIV.

It’s important to know that people can transmit HIV before seroconversion.

The time between exposure and the immune system’s initial response is a period of “acute HIV infection.” Following the initial transmission, the amount of HIV in the body is extremely high. So is the risk of transmitting the virus. That’s because the body has yet to manufacture the antibodies needed to fight it, and it’s not yet receiving treatment.

During this stage, most people have no idea that they’ve contracted HIV. Even if they’ve been tested, they may have received a false negative result. This might lead to engaging in practices with known risk factors, such as sex without a condom, where a person could unknowingly spread the virus to other people.

Anyone who thinks they’ve had a recent exposure should tell their healthcare provider. They may check the HIV viral load or prescribe preventive treatment for a month.

Anyone who thinks they may have been exposed to HIV should get tested. If the initial test results are negative, schedule a follow-up test.

Ask a healthcare provider or contact the local department of public health to find out where to go for testing. Testing sites may offer either anonymous or confidential testing, depending on the laws in the state and local area. Anonymous means names are not recorded by the testing site, and only the person being tested has access to the results. Confidential means a healthcare provider has access to the results, and the results may be recorded in a person’s medical file at the testing site.

Talk to a healthcare provider about post-exposure prophylaxis and pre-exposure prophylaxis.

People’s actions can help stop the spread of the virus. Until someone is confident that they’re HIV-free, they should avoid sexual contact or use a condom during sex. It’s also important to avoid sharing needles with others.

To find a nearby HIV testing site, visit GetTested.cdc.gov.

The Centers for Disease Control and Prevention (CDC) recommend that all people between the ages of 13 and 64 be tested at least once for HIV. People with known risk factors should be tested yearly, or more frequently.

HIV tests are very accurate, but no test can detect the virus immediately after transmission. How soon a test can detect HIV depends on what the test is looking for—antibodies, antigens, or the virus itself.

HIV testing uses a blood draw, a finger stick, or an oral swab. The type of sample used depends on the test.

These three types of diagnostic tests are used to detect HIV:

  • Antibody test. This test looks for the presence of HIV antibodies, or proteins that the body produces when an HIV infection is developing. Most HIV rapid tests and HIV home tests use antibody detection. A blood draw, finger prick, or oral swab may be used for this test.
  • Antigen/antibody tests. Antigens are substances that trigger the immune system when the HIV virus is in the acute infection stage. Antigens are released before antibodies are developed, so this type may be used for earlier detection. This test can also use a blood draw, finger prick, or oral swab.
  • Nucleic acid test (NAT). An expensive option, a NAT can search for the virus genetic material itself in blood samples. This test is typically saved for confirming a positive diagnosis or for people with a high risk of exposure or several known risk factors. A NAT typically uses a blood sample or an oral swab taken from the inside of the cheek.

Antibody and antigen/antibody tests are typically used first because they are less expensive and easier to administer. They may also detect signs of HIV sooner. A NAT test may be used to confirm a positive result on an antibody or antigen/antibody test, or if these tests are negative and there is a strong suspicion for new HIV infection.

Home Tests for HIV

Home testing is highly encouraged for its convenience and confidentiality. In fact, one study found that home testing encouraged adherence to the recommendation for regular testing, especially in populations with known risk factors.

Mail-in HIV tests use a blood sample from a finger prick. The sample is mailed to a licensed laboratory for testing, and results may be available in as little as one business day.

Rapid home tests offer accurate results in as little as 20 minutes from the comfort of home. Oral fluid samples are used most often.

Look for home HIV testing kits that are FDA approved. Reputable HIV home tests often come with confidential counseling and a referral service to help individuals follow up for additional testing in the event a test is positive.

A person who tests positive for HIV should discuss treatment with their current primary care provider, or they can ask the staff who performed the HIV test for a referral for HIV care and treatment.

Don’t wait to begin treatment. Early diagnosis, and earlier and more effective treatment options are helping people with HIV live longer and healthier lives than ever before. Current U.S. guidelines recommend starting treatment right away after testing positive to preserve the immune system.

A healthcare provider will prescribe medications to treat HIV. They can also provide information about known risk factors. It’s also important for a person who has tested positive to notify anyone they’ve had sexual contact with, so they can be tested too. It’s also important to use condoms to avoid passing the virus onto others.

Studies have shown that a person living with HIV who is on regular antiretroviral therapy that reduces the virus to undetectable levels in the blood is NOT able to transmit HIV to a partner during sex. The current medical consensus is that “Undetectable = Untransmittable.”

Anyone who suspects they’ve been exposed to HIV should not wait to act. They should make an appointment with a healthcare provider, tell them when they might have been exposed, and get an HIV blood test.

Keep in mind, timing matters. No test can detect an HIV infection immediately after contracting the virus. It may take up to 12 weeks for HIV antibodies to become detectable in the blood.

If a person receives a negative result on their first test, they should ask their healthcare provider if and when they should schedule a follow-up test.

And remember, it’s possible to pass the virus on to others, even before it becomes detectable, and even after starting on anti-viral medications, until the virus has been reduced to undetectable levels. Take steps to protect others by practicing sex with a condom and avoiding shared needles.