Why You Have to Wait for an STI Blood Test

Learning that you have been exposed to a sexually transmitted infection (STI, previously referred to as a sexually transmitted disease, or STD) such as herpes or HIV can be frightening. 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 STIs, such as chlamydia and gonorrhea, relatively quickly after infection using a highly sensitive urine test, this is not the case with all STIs.

Any STI test that detects an infection using antibodies can't be accurate for at least several weeks after exposure. It may be six months or more before you can trust a negative result. The unfortunate truth is that STI results take time. This article will review how long and why you have to wait for results and what you can do if time is a concern.

Why You Have to Wait

Many STI tests, particularly those for viral STIs 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 STI, 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 STI and tell whether you have it. However, these specific antibodies take time to develop.

How Long Does an STD Blood Test Take?

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

Many antibody tests look for immunoglobulin G (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 (results that tell you that you do not have the disease, when actually you do). 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 healthcare provider about what type of testing may be right for you.

Once you get a test, the turnaround time for test results also varies. Some rapid STI tests can give results within an hour. Other STI results make take up to two weeks to come in. This varies both by what test is used and what facilities your healthcare provider's office uses.

Some healthcare providers need to send out blood and urine samples to be tested. Others can run the tests in-house. These factors can have a significant effect on STI test result time.

What to Do If You Just Can't Wait

If you have a known, recent exposure to HIV, special testing may be available. These acute tests are designed to detect a new infection. However, not all healthcare providers will have access to these tests. They may need to send you to a more specialized clinic or lab.

If you think you have been exposed to herpes—especially if you have symptoms—see a healthcare provider as soon as symptoms appear. Antibody tests take a while to become accurate. If your provider can perform a viral culture on your sores, you can get results a lot sooner.

For a viral culture to work, your healthcare provider must 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 healthcare provider may be able to give you a presumptive diagnosis based upon the appearance of your outbreak.