HIV antibodies at 3 or 6 months

(1) Dear Alice,

What is the percentage of people who develop enough antibodies for HIV virus in the first three months after exposure? Does the length of window period depend only on the response of one's immune system or also on the amount of infectious fluid that was transferred during sex?

— Interested

(2) Dear Alice,

My question is about AIDS/HIV: I had a sexual affair that lasted two-and-a-half months, and, unfortunately, I was not using condoms. I happen to know nothing about my partner's previous sex life. I know that, for a test to show something, you must wait for six to nine months. I would like to know whether, provided that I am infected, I will experience any symptoms in this six to nine month period? Is it possible to have the virus and not have any symptoms or indications all this time? Right now, I am a graduate student and I am experiencing anxiety, fatigue, sleepiness, weight loss (three to five pounds in the last two months). Are these related to the disease, or is it just in my mind?

Grateful to you,

Thank you in advance,

Dear Interested and Wrongdoer,

When it comes to charting out a timeline for HIV tests and potential symptoms, the short answer to your questions are… it depends. There are actually several types of tests out there, and each one detects HIV in a person’s body at a different time after exposure. Some tests, called antibody screening tests (or immunoassays), work by detecting antibodies that a person’s body produces in response to the virus. Antibody production takes about three to twelve weeks after exposure. This time between exposure and when a detectable number of antibodies are produced is called the “window period.” So, an antibody screening test wouldn’t be able to “see” the HIV until after the window period. A different type of HIV test, called an antigen test, actually looks for particles of the virus itself. Because of this, the antigen tests can detect the virus before the window period is even over — as soon as two weeks after exposure. During this window period, about 50 percent of people experience something called conversion sickness, which are flu-like symptoms that can occur in the first few weeks or months of infection.

Here are some details about each of the tests currently in use, which can give you a sense of how soon after exposure the virus can be diagnosed:

  • Antibody screening test (immunoassay): For this test, you give a sample of oral fluid or blood, which is then tested for HIV antibodies. Keep in mind that it takes the body several weeks or even months to produce those antibodies, so immunoassays used in most labs today (known as third generation) can detect the virus about 23 days after exposure.
  • Antigen test: Most antigen tests are combined with antibody screenings, so this test (known as fourth generation) looks for both the particles of the HIV virus as well as antibodies. It is able to detect HIV as soon as 14 to 20 days after exposure.
  • Home-tests: There are two HIV tests currently approved by the FDA for use at home (OraQuick and Home Access). Although they give results quickly, these tests require a follow-up test in a lab to confirm a positive result. At-home tests (as well as “rapid tests” which you might see in use outside of clinics) can detect the virus 28 to 48 days after exposure.

As your questions suggest, the general guideline is to use three months (about 90 days) after exposure as the testing benchmark. That’s because research shows that 97 percent of people will have produced enough antibodies to accurately test positive within three months. Sometimes, it takes people as long as six months to test positive, but this is rare. Interested, you also ask about whether the amount of infected fluid during exposure can affect the window period. While there’s not a lot of research in that area, researchers do know that the virus reproduces itself very rapidly once it’s inside the body, so the initial amount of fluid someone’s exposed to would not likely impact their window period. However, during the first ten weeks of infection, the virus is much more transmissible (up to 26 times more infectious!), so getting tested early can be a safe move.

Because everyone’s window period is different — and because the tests are different — it’s recommended that you test before the three month mark, you get re-tested for HIV after three months if you got a negative test result at first. Or, people who are exposed to HIV frequently may prefer to get tested with increased regularly — say, every few months. Getting tested for HIV can be stressful and emotional, but becoming familiar with the timelines of the different types of tests can alleviate some of the anxiety. The Go Ask Alice! HIV/AIDS archives have lots of info on transmission, symptoms, testing, treatment, and prevention.

Last updated Mar 26, 2015
Originally published Mar 14, 1996

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