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
| By | Healthwise Staff |
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| Primary Medical Reviewer | Sarah Marshall, MD - Family Medicine |
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| Specialist Medical Reviewer | Jeanne Marrazzo, MD, MPH - Infectious Disease |
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| Last Revised | December 15, 2010 |
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