Sexual Conditions Health Center

Chlamydia tests use a sample of body fluid or urine to see whether chlamydia bacteria (Chlamydia trachomatis) are present and causing an infection. Chlamydia is the most common bacterial sexually transmitted infection (STI) in the United States.

Several types of tests can be used to find a chlamydia infection. Most tests use a sample of body fluid from the affected area.

• Nucleic acid amplification tests (NAAT). These tests find the genetic material (DNA) of chlamydia bacteria. These tests are the most sensitive tests available. That means they are very accurate and that they are very unlikely to have false-positive test results. A polymerase chain reaction (PCR) test is an example of a nucleic acid amplification test. This test can also be done on a urine sample.
• Nucleic acid hybridization tests (DNA probe test). A probe test also finds chlamydia DNA. A probe test is very accurate but is not as sensitive as nucleic acid amplification tests.
• Enzyme-linked immunosorbent assay (ELISA, EIA). This quick test finds substances (chlamydia antigens) that trigger the immune system to fight chlamydia infection.
• Direct fluorescent antibody test (DFA). This quick test also finds chlamydia antigens.
• Chlamydia culture. A culture is a special cup that allows the chlamydia bacteria to grow. This test is more expensive, and the results take longer (5 to 7 days) than the other tests. The culture must be done in a lab.

Why It Is Done

A test for chlamydia is done to:

• See whether symptoms of a sexually transmitted infection (STI) are caused by a chlamydia infection.
• Check people who are at high risk for being infected with chlamydia. A chlamydia infection does not always cause symptoms. The U.S. Preventive Services Task Force (USPSTF) recommends checking for chlamydia for:
  • All sexually active women age 24 or younger.
  • Women older than age 24 with high-risk sexual behaviors.
  • All pregnant women in the first trimester and again in the third trimester if high-risk sexual behaviors are reported. Treating a pregnant woman who has a chlamydia infection can prevent an infection in her newborn.
  • All women with pelvic inflammatory disease (PID).
  • All women with symptoms of a cervical infection (cervicitis) found on a pelvic exam.
• Check for infection in a newborn whose mother had a chlamydia infection at the time of delivery.

How To Prepare

A chlamydia test is done on either fluid (direct sample) collected from the area of the body that is most likely to be infected or on a urine sample. If your chlamydia test is being done on a:

• Direct sample (usually from the cervix): A woman should not douche or use vaginal creams or medicines for 24 hours before having a chlamydia test.
• Urine sample: Do not urinate for 2 hours before a urine sample is collected.