Why You Have to Wait for an STD Blood Test

How Antibody Tests for Herpes, HIV, and Other STDs Work

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Learning that you have been exposed to a sexually transmitted disease (STD) such as herpes or HIV can be frightening. It doesn't matter whether a former sexual partner calls to tell you they're infected or you hear from the health department that you need to be tested. It's scary to learn that you may be at risk.

Although it's possible to test for some STDs, such as chlamydia and gonorrhea, relatively quickly after infection using a highly sensitive urine test, this is not the case with all STDs.

Any STD test that detects an infection using antibodies can't be used for at least several weeks, and it may be six months or more before you can trust a negative result.

Why You Have To Wait

Many STD tests, particularly those for viral STDs such as herpes and HIV, do not look for the infection itself. Instead, they look for your body's reaction to the infection, specifically your antibody response.

When you are exposed to or infected with an STD, your immune system will try to fight off the pathogen. Part of this process involves making antibodies against the infectious agent. These antibodies are specific to whatever you are infected with. That's how a blood test can look for antibodies to a specific STD and tell whether or not you have it. However, these specific antibodies take time to develop.

How much time it takes for you to make detectable amounts of antibodies against your infection depends upon a number of factors, including:

  • whether you've been infected with same pathogen before
  • how active the infection is
  • how much of the pathogen entered your body
  • the overall health of your immune system
  • what type of antibody the test is looking for

The soonest a test might have a reasonable chance of detecting an antibody response is two weeks, and that is only true for tests that look for a specific early type of antibody called IgM.

Many antibody tests look for IgG, which takes longer to develop. Furthermore, even an IgM test cannot be counted on to be accurate at such an early point after infection.

Within the first few months, there is a very high risk of false negative test results. This risk goes down over time. By six months after infection, most people will turn positive on an antibody test.

Because of this, antibody testing isn't appropriate for people who are worried they may have been very recently exposed to HIV or herpes. If this is the case, talk to your doctor about what type of testing may be right for you.

What Should You Do If You Just Can't Wait?

If you have a known, recent exposure to HIV, special testing may be available to detect a new infection, although not all physicians will have access to it.

If you think you have been exposed to herpes and you have symptoms, go to your doctor as soon as symptoms appear. Although the antibody tests take a while to become accurate, if your doctor can perform a viral culture on your sores, you can get results a lot sooner.


 
For a viral culture to work, your doctor has to be able to isolate the active virus from your sores. There is only a short window when that is possible after the beginning of an outbreak. If you are tested after your sores have begun to heal, there is a possibility of a false negative test. However, your doctor may be able to give you a presumptive diagnosis based upon the appearance of your outbreak.

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