The test is used:

1. to diagnose the cause of symptoms,
2. to screen sexually active people for the microorganism, or
3. to document that a person has been sexually abused.

A definitive diagnosis is important because the symptoms of chlamydia can resemble those of gonorrhea and the two infections require different antibiotic treatment.

The preferred method of testing currently is the molecular test also known as nucleic acid amplification tests (NAAT). This test is based on amplification of the DNA that is present in Chlamydia trachomatis. Molecular testing for Chlamydia trachomatis is currently the standard and is widely utilized. The advantage of molecular tests is that they are generally more sensitive and specific than conventional culture and can therefore identify more positive specimens. However, molecular tests should not be used to diagnose or verify cases with legal implications. Until the legal system changes, only a positive culture result proving infection with chlamydia is admissible in court. All positive molecular tests for Chlamydia trachomatis should be verified by the same or another methodology for confirmation. Molecular tests need to be validated for different sources of specimens. They have not been FDA-approved for performance with ocular (eye), pharyngeal (throat), or rectal sites.

Other methods that may be used include direct fluorescent antibody stain (DFA), which detects chlamydia antigens, and DNA probe, another test that looks for chlamydia DNA but is less sensitive than NAAT. A newly developed rapid assay is also being evaluated. The rapid method recognizes markers from the bacteria in specimens that can be self-collected vaginal swabs or swabs collected by health care providers and can generate results within 30 minutes (see In the News: Rapid Test Screens for Chlamydial Infections).

Testing for Neisseria gonorrhoeae (gonorrhea) and Chlamydia trachomatis is generally done simultaneously as the two organisms have similar clinical presentations.

A doctor may order a chlamydia test if you have symptoms such as vaginal discharge and abdominal pain (for women) or unusual discharge from the penis or pain on urination (for men). However, because many infected people do not have any symptoms, the U.S. Preventive Services Task Force recommends the following:

• All sexually active females 25 years of age and younger should have a chlamydia test once a year. If you are pregnant and 25 years old or younger, you should be tested for chlamydial infection.
• All other sexually active women who have no symptoms but are at increased risk for infection should be routinely screened.

The U.S. Centers for Disease Control and Prevention (CDC) also recommend annual screening of sexually active women 25 years of age and younger and of women over 25 with risk factors, including a new or multiple sexual partners. The CDC also recommends screening of all pregnant women and testing at least once a year for males who have sex with other males.

Because symptoms of chlamydia can be similar to those of other STDs, other screening tests, such as for gonorrhea, may be performed along with the chlamydia test.

A positive test indicates an active infection that requires treatment with a course of antibiotics.

A negative test means only that there is no evidence of disease at the time of the test. It is important for those who are at increased risk of infection to have screening tests performed on a regular basis to check for possible exposure, especially since re-infection is common, particularly among teenagers.

If you are infected, your sexual partner(s) should also be tested and treated as well.

People who are infected have a higher risk of developing other sexually transmitted diseases, including a 3 to 5 times greater risk of acquiring HIV if exposed to it.