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 diseases (STD) 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. This 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 common, quick test finds substances (chlamydia antigens) that trigger the immune system to fight chlamydia infection.
- Direct fluorescent antibody test (DFA). This common, 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. The chlamydia culture test may be done when child sexual abuse is suspected or when treatment for infection has not worked.
Why It Is Done
A test for chlamydia is done to:
- See whether symptoms of a sexually transmitted disease (STD) 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 25 or younger.
- Women older than age 25 with high-risk sexual behaviors.
- All pregnant women in the first trimester and again in the 3rd 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 health professional 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 examination table with your feet raised and supported by stirrups. This allows your health professional to examine your vagina and genital area. Your health professional 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 health professional 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 examination. 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 diseases (STDs) may be needed to find the cause of symptoms. |
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| Abnormal: | Chlamydia antigens or DNA are found. If a culture is done, chlamydia bacteria grow in the culture. |
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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.
