Are STD Test Results Always Right?

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Couple Consulting with Doctor. Bernard van Berg / Getty Images

Question: Are STD Test Results Always Right?

There are several reasons why STD screening isn't an infallible way to avoid STDs. I would never want to discourage people from regular STD screening. It is one of the best things you can do to reduce your risk of acquiring an STD (along with practicing safe sex), but it isn't perfect.

Part of taking responsibility for your sexual health is acknowledging that even if you do everything right, sexual activity still has risks.

 Condoms and dental dams can sometimes fail. STD tests don't always give the full picture. 

People often think that if they come away from their annual doctor's visit with a clean bill of health, they don't need to worry about whether they have an STD. That's a dangerous misconception, for a number of reasons. Here are some reasons that, even your doctor calls to say you're fine, you may still occasionally end up asking yourself, "Do I have an STD?"

  1. You didn't actually get tested
    A lot of people think that their doctor screens them for STDs as part of their annual exam. This is, sadly, untrue. Many doctors don't regularly screen their clients for STDs, even when practice guidelines say they should. The only way to be certain you're getting tested for STDs is to ask your doctor to test you - and give them a list of what you want to be tested for. Remember, your clean STD test results only show that you're negative for diseases you actually got tested for. Even then, it's possible that...
  1. You got tested too soon
    Some STD tests are not effective for a newly acquired infection. Recent studies have, for example, shown that the standard blood test for syphilis is ineffective at detecting early cases of the disease. The types of HIV tests and other STD tests that look for an antibody response instead of hunting for the pathogen itself may be particularly susceptible to this problem. It takes time for an antibody response to develop.
  1. The test gave an inaccurate result
    When designing a diagnostic test, there is always a trade-off between sensitivity and specificity. Almost no test is going to be perfectly able to determine whether or not someone is infected. How accurate are STD tests? Well, their ability to predict your health is  dependent, in part, on the population that test is being used in (see this example about the accuracy of herpes blood tests.) Most tests are designed to be pretty good, and there are almost always ways to make their diagnoses more accurate. Still, both false positives and false negatives can be a problem. Which problem you need to worry about depends on the disease in question and the test that is being used to detect it.
  2. You were given the wrong test
    There isn't always a right test, but sometimes there is a wrong one. As mentioned above, every diagnostic test has trade-offs. There are often tests that are more or less accurate depending on the circumstance and the population. The problem is that the best test isn't always available or practical. Therefore, doctors will sometimes end up having to use a less accurate method of diagnosis.
  3. Doctors don't test for what you have
    There are some diseases for which there are no commercial tests, or for which doctors simply do not bother to test. Why? Either because the disease is uncommon or because it is unlikely to cause serious problems if left untreated. For example, doctors don't test for molluscum contagiosum, because they assume that anyone infected will have symptoms and because an infection will usually run its course without any serious side effects.

    On the other hand, doctors are probably unlikely to test for rectal chlamydia, anal cancer, and other rectal STDs for other reasons.They may not offer the tests because of the relative rarity of these conditions. They also might not offer them if they are uncomfortable asking the sexual history questions that would allow them to determine that someone is at risk. Even when reasonably accurate tests are available, they don't do any good if they're not being used.

    A Word from Verywell

    Regular STD screening is an important tool for reducing the likelihood that someone will have an undetected, and untreated STD that they could transmit to others. However, it's important to remember that regular STD testing and consistently practicing safe sex doesn't make sex a risk-free activity. Lower risk, yes. But STD tests aren't 100% effective. Neither is safe sex. 

    With proper precautions, sex is a relatively low-risk way to experience pleasure and connection and show your affection for someone. That doesn't mean sex can't have consequences. Part of being responsible for your sexual health is keeping those potential consequences in mind.

    STD testing is a great tool for making better decisions about what levels of risk you personally find acceptable in any given situation.

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