Can a Chlamydia Test Be a False Positive?

A positive chlamydia result can come as a shock, especially if you feel fine, have been faithful or have just finished treatment. It’s natural to ask whether the test got it wrong. A wrong result is possible in some situations, but a positive should never be brushed off without talking to a clinician.

Can a chlamydia test be a false positive?

Yes, it can, though the sources we checked name one situation clearly: testing too soon after treatment. The CDC says that using a chlamydia NAAT (nucleic acid amplification test) less than 4 weeks after finishing therapy is not recommended, because “nonviable organisms” that remain can lead to false-positive results.

Outside that situation, the CDC and WHO describe NAATs as the most sensitive and recommended way to detect chlamydia. The pages we reviewed don’t give a false-positive rate, so we can’t tell you how often it happens. Treat a positive as likely correct until a clinician tells you otherwise.

How accurate are chlamydia tests?

The WHO calls NAATs the gold standard for diagnosing chlamydia. The CDC says they are the most sensitive tests for the usual samples and the recommended test.

The best sample depends on the person:

• People with a vagina: a vaginal swab is the preferred sample. The CDC says swabs collected by the patient are as sensitive and specific as those collected by a clinician.
• People with a penis: a first-void urine sample or a urethral swab.
• Throat or rectum: a swab from the site of exposure.

The WHO notes that urine samples are less sensitive than swabs from the genital, anal and throat sites. This is mostly about missing an infection (a false negative), which is a different problem from a false positive.

What if I tested positive just after finishing treatment?

If you finished antibiotics less than 4 weeks before the test, the result may reflect dead bacteria rather than a new infection. Tell your clinician exactly when you finished.

The CDC says repeat testing right after treatment is generally not advised, unless you didn’t take the medicine as prescribed, symptoms persist, or you may have been re-exposed. In that case your clinician may suggest a repeat test. Otherwise, the standard check is about 3 months after treatment.

The CDC also says that most infections found after treatment are not treatment failures but reinfections, from a partner who wasn’t treated or a new partner. If you’ve had sex with someone who hasn’t been treated, a positive result may be real.

What if my throat swab was positive?

Sometimes a throat swab done for gonorrhea also picks up chlamydia. The CDC says the importance of chlamydia in the throat is unclear, but that if it is found, it should be treated, since it can pass to the genitals. Your clinician will advise you.

I tested positive in a long relationship. What does that mean?

It can be upsetting, but try not to jump to conclusions. The CDC says chlamydia often has no symptoms, and the NHS says that when symptoms do occur they can start anywhere from a week to several months after infection. A positive result on its own can’t answer questions you may have about a relationship.

What should I do now?

• Talk to the clinician who gave you the result. Ask what the test was, when it was taken and whether a repeat is sensible.
• Don’t skip treatment because you suspect an error. The CDC says treatment delays have been linked to complications such as pelvic inflammatory disease in a small proportion of women.
• Order tests for HIV, gonorrhea and syphilis too.
• Tell recent partners so they can be tested. They can order an online STD test, and a doctor or clinician can help you contact them. See chlamydia treatment and retesting for how partner treatment works.

If you are pregnant, the CDC advises treatment and a repeat test about 4 weeks later, because chlamydia that persists can seriously affect mothers and newborns.