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 Canada.
Several types of tests can be used to find a chlamydia infection, but the Public Health Agency of Canada (PHAC) recommends a nucleic acid amplification test (NAAT) be used whenever possible. 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 very good at identifying chlamydia. A test that is positive almost always means the problem is there and is unlikely to be a false-positive test result. 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. This is a test to find the bacteria that cause a chlamydia infection. A sample of body fluid from areas such as the cervix, urethra, eye, rectum, or throat is added to certain cells used to grow chlamydia. If no chlamydia bacteria infect the cells, the culture is negative. If chlamydia bacteria infect the cells, the culture is positive. Results take longer (5 to 7 days) than the other tests.
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 Public Health Agency of Canada (PHAC) recommends checking for chlamydia for:
- All sexually active women age 25 or younger.
- Women and men with high-risk sexual behaviours.
- All pregnant women in the first trimester and again in the third trimester if high-risk sexual behaviours are reported. Treating a pregnant woman who has a chlamydia infection can prevent an infection in her newborn.
- 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 a urine sample or fluid (direct sample) collected from the area of the body that is most likely to be infected. If your chlamydia test is being done on a:
- Urine sample: Do not urinate for 2 hours before a urine sample is collected.
- 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.
How It Is Done
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.
- 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 examination table with your feet raised and supported by stirrups. This allows your doctor to examine your vagina and genital area. Your doctor will insert a lubricated 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.
There is also a self-test for women to collect a sample from their vagina and bring it to the lab for testing.
In rare cases, a throat culture may be done.
How It Feels
There is no discomfort in collecting a urine sample.
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.
There is no chance for problems in collecting a urine sample.
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.
Chlamydia tests use a sample of body fluid or urine to see whether chlamydia bacteria ( Chlamydia trachomatis) are present and causing an infection.
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.
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:
- Stool with the rectal sample.
- Using antibiotics 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.
- Screening for and treating chlamydia can help prevent pelvic inflammatory disease (PID). To learn more about 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.
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.
Current as of: February 26, 2020
Author: Healthwise Staff
Sarah Marshall MD - Family Medicine
Thomas M. Bailey MD - Family Medicine
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
Devika Singh MD, MPH - Infectious Disease