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Chlamydia Tests


Test Overview

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.

How It Is Done

Direct sample

In a direct sample, a sample of body fluid is taken from the affected area. In adults, these areas may include the cervix, urethra, rectum, or eye.

  • For men. To collect a sample from the urethra or rectum, your doctor will insert a swab into the opening of your urethra or rectum to collect a sample. A sample from the urethra is more likely to detect chlamydia if a man has not urinated for at least 2 hours before the sample is taken.
  • For women. To collect a sample from the cervix, you will take off your clothes below the waist and drape a cloth around your waist. You will lie on your back on an exam table with your feet raised and supported by stirrups. This allows your doctor to examine your vagina and genital area. Your doctor will insert an instrument with curved sides (speculum) into your vagina. The speculum gently spreads apart the vaginal walls so the inside of the vagina and the cervix can be looked at. Samples are collected from the cervix with a swab or small brush.
  • To collect a sample from your eye, your doctor will gently brush the insides of your lower and upper eyelids with a swab.

In rare cases, a throat culture may be done.

Urine sample

If a urine sample is collected for nucleic acid amplification testing (such as PCR testing), do not urinate for 2 hours before the test. Do not wipe the genital area clean before urinating. Collect the first part of your urine stream, immediately as you begin urinating.

How It Feels

Collecting a sample of fluid from the urethra, anus, or rectum may cause mild discomfort or pain.

Collecting a sample from the cervix may cause mild discomfort. Most women find that the procedure feels like a Pap test or pelvic exam. Some women feel some cramping when the speculum is inside the vagina.

Collecting a sample from the eye is painless unless the eyelids have sores on them.

Risks

There is very little chance of problems when collecting a sample of fluid from the cervix, urethra, rectum, eyes, or throat.

In rare cases, a person may suddenly get dizzy or feel faint (called vasovagal syncope) because of fear or pain when the swab is inserted into the urethra.

Results

Chlamydia tests use a sample of body fluid or urine to see whether chlamydia bacteria (Chlamydia trachomatis) are present and causing an infection.

Chlamydia tests
Normal:

No chlamydia antigens or DNA are found. If a culture is done, no chlamydia bacteria grow in the culture. More tests for other sexually transmitted infections (STIs) may be needed to find the cause of symptoms.

Abnormal:

Chlamydia antigens or DNA are found. If a culture is done, chlamydia bacteria grow in the culture.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Urinating before (within 2 hours of) collecting a urine sample or a sample of fluid from the urethra.
  • Stool with the rectal sample.
  • Using antibiotics before the test.
  • Douching or using vaginal creams or medicines 24 hours before the test.

What To Think About

  • If a chlamydia infection is suspected, do not have sexual intercourse until the test results have come back. If you have a chlamydia infection, do not have sexual intercourse for 7 days after the start of treatment. Your sex partner(s) should also be treated for a chlamydia infection so that you don't get reinfected and so that others don't get infected.
  • Only one laboratory test (NAAT, ELISA, DFA, DNA probe testing, or chlamydia culture) is needed to diagnose chlamydia. Your doctor can choose which test to use.
  • Your doctor is required to report your chlamydia infection to the state health department. The department may contact your sex partners to inform them that they also need treatment.
  • Screening for and treating chlamydia can help prevent pelvic inflammatory disease (PID). For more information on the treatment of a chlamydia infection, see the topic Chlamydia.
  • Other sexually transmitted infections may be present at the same time as chlamydia, so it is important to be tested and treated for all STIs. Chlamydia as well as other STIs can also increase the chance of getting human immunodeficiency virus (HIV). An HIV test may be offered at the same time as a test for chlamydia or other STIs.

References

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.

  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

Credits

ByHealthwise Staff
Primary Medical ReviewerSarah Marshall, MD - Family Medicine
Specialist Medical ReviewerJeanne Marrazzo, MD, MPH - Infectious Disease
Last RevisedDecember 15, 2010

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