eg. Can you get STD from giving your partner a BJ?

The likliness of getting a false negative on an STD screening?

Asked by on October 23, 2013

Is it more likely to get a false negative or a false positive on an STD screening, for Chlamydia for example, a urine test?

I had Chlamydia, took Azithromycin, 1 month after taking Azithromycin I got retest, another urine test. The result came up negative this time.
The nurses say, its definitely negative and that they usually don’t even have patients retest.
But I am hoping the negative test result I got is accurate and is not a false negative, so I didn’t know whether to get retested a 2nd time to confirm that it’s negative for sure?

And I haven’t had sex in months or during the treatment, so no chance of reinfection.




Bob B

October 23, 2013 at 6:04 pm

Depends a bit on the specific test you had, but STD screening is a very well-established procedure, and the chances of a false positive or false negative are extremely low. And false negatives are generally less likely than false positives- usually, a negative initial screen is enough to rule out the disease, whereas a positive test is confirmed with a second, more specific one, to ensure it is definitely a positive.

So basically, the chances of you still being infected are negligible. Obviously, no test is 100% perfect, however they are sufficiently robust that you can be assured of their results. If you tested positive, had treatment, and tested negative afterwards, by far the most likely conclusion is that the treatment cured the infection and you are no longer infected.



September 21, 2016 at 11:59 am

Bob’s answer is actual very inaccurate. In medicine in general, he would be right, but not with the type of STD you are talking about.

False negatives for urine tests of bacterial infections, such as chlamydia and gonorrhea have false negatives 10% of the time. In science, we don’t consider anything with that high of an error rate trustworthy or accurate at all, just think about the ramifications of 10% of people thinking they are disease free, infecting others.

For a test to be considered accurate, it should be accurate at least 9,999 out of 10,000 times, or 99.99% of the time. In scientific fields like physics, we often aim for accuracies like 99.999999% of the time, or wrong 1 in 100,000,000 times.

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