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Chlamydia

Formal name: Chlamydia trachomatis culture; Chlamydia trachomatis DNA Probe; Chlamydia trachomatis by Amplified Detection; Chlamydia trachomatis by Direct Antigen Detection (DFA)
Related tests: Gonorrhea

At a Glance

Why Get Tested?

To screen for or diagnose chlamydia infection

When to Get Tested?

If you are sexually active, pregnant, have one or more risk factors for developing chlamydia, or have a symptoms, such as vaginal discharge and abdominal pain (for women) or unusual discharge from the penis or pain on urination (for men); depending on your risk factors, may be annually

Sample Required?

A swab or brush of cells or secretion from the infected area; urine (male or female) for the molecular test

Test Preparation Needed?

None

The Test Sample

What is being tested?

The test is looking for evidence of infection by the bacterium Chlamydia trachomatis. Chlamydia is the most common bacterial sexually transmitted disease (STD) in the United States and is especially common among people 15 to 25 years of age. It is estimated that 3 million Americans are infected with chlamydia each year, although this number may be higher. Since many people do not experience any symptoms, cases often go undiagnosed and unreported; still, over 1 million new cases are reported each year. Diagnosing and treating chlamydia is very important to prevent long-term complications and spread of the infection to others.

Chlamydia is generally transmitted through sexual contact (oral, vaginal, or anal) with an infected partner. Risk factors include having multiple sex partners, coinfection or previous infection with another STD, and not using barrier contraception consistently. An infected mother can spread the disease to her baby during childbirth. These babies are in danger of developing conjunctivitis, an inflammation that can threaten eyesight, and pneumonia.

About 75% of infected women and 50% of infected men have no symptoms; some may experience only mild symptoms. For women, symptoms, if they occur, include bleeding between menstrual periods and after sexual intercourse, abdominal pain, painful intercourse, and an abnormal vaginal discharge. For men, symptoms include pus or milky discharge from the penis and inflammation of the prostate (prostatitis) or of the rectal area (proctitis). Both sexes can experience painful or frequent urination.

Chlamydia is easily treated with a course of antibiotics, but if left untreated, it can cause severe reproductive and other health problems. If left untreated, 40% of women may develop pelvic inflammatory disease (PID) from infections that start on the cervix but that can spread to the fallopian tubes and ovaries. This can cause infertility and increase the risk of tubal (ectopic) pregnancy, which is often fatal. Women who are infected and pregnant may experience heavy bleeding before delivery and premature rupture of the membranes. Men, too, may become sterile. Both sexes may develop rectal itching and red, swollen, itchy eyes.

How is the sample collected for testing?

Generally, your doctor will use a swab or brush to take a cell sample or secretion from the infected area, such as the cervix, urethra, penis, anus, or throat. Urine specimens are acceptable if the particular lab where the sample is sent uses a molecular method that is validated for this sample.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?

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.

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When is it ordered?

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 recommends 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.

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What does the test result mean?

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.

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Is there anything else I should know?

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.

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Common Questions

1.  How long does it take to get results?

This will depend on the method used to diagnose the infection. The turn-around time for a culture is typically 5 to 7 days. Other methods can give results in one day, taking several hours. A rapid test that gives results in 30 minutes is being studied but is not yet available in the U.S. (See In the News: Rapid Test Screens for Chlamydial Infections).

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2.  How can chlamydia be prevented?

The American Social Health Association has information on things people can do to reduce their risk.

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Ask a Laboratory Scientist

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

Planned Parenthood. Chlamydia. Available online at http://www.plannedparenthood.org/health-topics/stds-hiv-safer-sex/chlamydia-4266.htm through http://www.plannedparenthood.org. Accessed February 2009.

Centers for Disease Control and Prevention. Chlamydia - CDC Fact Sheet. Available online at http://www.cdc.gov/std/Chlamydia/STDFact-Chlamydia.htm through http://www.cdc.gov. Accessed February 2009.

TeensHealth. Chlamydia. Available online at http://kidshealth.org/teen/sexual_health/stds/std_chlamydia.html through http://kidshealth.org. Accessed February 2009.

ARUP Consult. Sexually Transmitted Infections, Bacteria. Available online at http://www.arupconsult.com/Topics/InfectiousDz/Bacteria/STIs.html# through http://www.arupconsult.com. Accessed February 2009.

WebMD. Chlamydia Tests. Available online at http://www.webmd.com/sexual-conditions/chlamydia-tests through http://www.webmd.com. Accessed February 2009.

Sources Used in Previous Reviews

Centers for Disease Control and Prevention. Chlamydia Fact Sheet. Available online at http://www.cdc.gov/std/Chlamydia/STDFact-Chlamydia.htm through http://www.cdc.gov.

Arnot Ogden Medical Center. Chlamydia. Available online at http://www.aomc.org/chlamydia.html through http://www.aomc.org.

American Social Health Association. Learn Chlamydia Facts. Available online at http://www.ashastd.org/learn/learn_chlamydia_facts.cfm through http://www.ashastd.org.

Centers for Disease Control and Prevention. Sexually transitted diseases treatment guidelines 2002. MMWR 2002;51 (No. RR-6) [32-41].