Chlamydia trachomatis nucleic acid amplification test
What is this test?
This test detects bacterial DNA gene sequences in certain body fluids. This test is used when an infection with a bacteria called Chlamydia trachomatis is suspected in the urinary and genital organs. A sample of endocervical cells, urethral cells or discharge, or clean urine may be collected for this test.
Why do I need this test?
Laboratory tests may be done for many reasons. Tests are performed for routine health screenings or if a disease or toxicity is suspected. Lab tests may be used to determine if a medical condition is improving or worsening. Lab tests may also be used to measure the success or failure of a medication or treatment plan. Lab tests may be ordered for professional or legal reasons. You may need this test if you have:
- Genitourinary chlamydia infection
When and how often should I have this test?
When and how often laboratory tests are done may depend on many factors. The timing of laboratory tests may rely on the results or completion of other tests, procedures, or treatments. Lab tests may be performed immediately in an emergency, or tests may be delayed as a condition is treated or monitored. A test may be suggested or become necessary when certain signs or symptoms appear.
Due to changes in the way your body naturally functions through the course of a day, lab tests may need to be performed at a certain time of day. If you have prepared for a test by changing your food or fluid intake, lab tests may be timed in accordance with those changes. Timing of tests may be based on increased and decreased levels of medications, drugs or other substances in the body.
The age or gender of the person being tested may affect when and how often a lab test is required. Chronic or progressive conditions may need ongoing monitoring through the use of lab tests. Conditions that worsen and improve may also need frequent monitoring. Certain tests may be repeated to obtain a series of results, or tests may need to be repeated to confirm or disprove results. Timing and frequency of lab tests may vary if they are performed for professional or legal reasons.
How should I get ready for the test?
Written consent will be required for endocervical sampling. Review the consent form with the healthcare worker and ask any questions that you have before signing the consent form.
Tell the healthcare worker if you have a medical condition or are using a medication or supplement that causes excessive bleeding. If possible, schedule the procedure one week after your menstrual period. Do not douche or have sexual intercourse for 24 hours before the procedure.
You may be asked to urinate prior to your endocervical sampling. This will make it easier for the healthcare worker to see your cervical canal during the procedure and may make the procedure more comfortable for you.
Before collection of urethral cells and/or urethral discharge for this test, you should not urinate during the hour prior to the test. This is because urine may minimize or clear your urethra (the tube that drains urine) of any organisms (germs), thus affecting the results of this test.
Urinate an hour or more before a sample is collected.
To prepare for giving a urine sample, be sure to drink enough fluids before the test, unless you have been given other instructions. Try not to empty your bladder before the test.
Urinate an hour or more before a sample is collected.
How is the test done?
A sample of endocervical cells, urethral cells or discharge, or clean urine may be collected for this test.
For an endocervical sampling, you will be asked to lie on your back with your legs spread and feet placed in stirrups. A speculum will be inserted into your vagina. This tool is used to gently spread apart your vagina. A small brush is inserted into the endocervical canal and rotated. This is done to collect cells. Once a sufficient sample is collected, the brush is removed. The sample off the brush is then sent for testing.
A urethral culture procedure is used to collect cells samples and/or urethral discharge. This test is usually done on males only. For this procedure, you will be asked to lie on your back. The tip of the penis will be cleaned. A special thin swab will be inserted into the urethra. The swab will gently be twisted side to side and then remain still for a few seconds before it is removed. This is to allow the swab to absorb enough fluid to be cultured. It may be possible to get a sample by “milking” the urethra for discharge. Ask the healthcare worker if this is an appropriate option.
Immediately before a test that requires a clean urine sample, males must clean, rinse, and dry the head of the penis. Females must clean, rinse, and dry the urethral area. As you begin urinating, allow a small amount of urine to go into the toilet, and then stop the urine stream. Position the container to collect your urine, and urinate into the container. Remove the container when it has a sufficient amount of urine in it, and finish urinating into the toilet.
The urine sample may also be collected from a urinary catheter. If a catheter is present, the healthcare worker will collect urine from the catheter for testing. If there is no catheter present, a catheter may need to be inserted temporarily to collect the sample. The area will be cleaned, and a sterile catheter will be inserted into your urethra. Urine will drain from the catheter into a container for the test. When sufficient urine has been collected, the catheter will be removed. A special bag may be used to collect a urine sample from an infant.
How will the test feel?
The amount of discomfort you feel will depend on many factors, including your sensitivity to pain. Communicate how you are feeling with the person doing the procedure. Inform the person doing the procedure if you feel that you cannot continue with the procedure.
You may feel mild discomfort, cramping, or pain during an endocervical sampling.
A urethral culture generally takes less than a minute. However, you may feel discomfort when the swab moves in the urethra.
There is usually no pain experienced when a clean-catch urine sample is given or when the sample is taken from an existing urinary catheter. If an intermittent (temporary) catheter is used to obtain the sample, you may feel some discomfort.
What should I do after the test?
After endocervical sampling, you may experience some light spotting (mild, occasional bleeding from the vagina). Generally, there are no activity restrictions after this procedure.
After a sample has been collected, avoid all sexual activities until you receive your results and speak to your healthcare worker.
After collecting a urine sample, close the container if it has a lid. Place the container where the healthcare worker asked you to put it. Clean your hands with soap and water.
What are the risks?
Endocervical cells: An endocervical cell sample is collected using a method similar to a Pap smear. This procedure may cause light bleeding from the vagina. If you have a medical condition, or are using a medication or supplement that causes excessive bleeding, you are at a higher risk of bleeding during or after this procedure. The person doing this procedure may need to perform it more than once. Talk to your healthcare worker if you have any concerns about the risks of this procedure.
Urethral cells/discharge: Ask the healthcare worker to explain the risks of this procedure to you before it is performed.
Clean urine: There are several different ways that may be used to collect a sample of clean urine. Urine may be collected by urinating in a cup using the clean-catch technique, or by collecting urine from an existing urinary catheter. Generally, there are no risks when collecting a clean urine sample using either of these methods. Another way to collect a clean urine sample is by inserting a temporary urinary catheter. Risks of using this method include bleeding, infection, catheter misplacement, and damage to the urethra or bladder. If you have a medical condition, or are using a medication or supplement that causes excessive bleeding, you are at a higher risk of bleeding. The person doing this test may need to perform it more than once. Talk to your healthcare worker if you have any concerns about the risks of clean urine collection.
What are normal results for this test?
Laboratory test results may vary depending on your age, gender, health history, the method used for the test, and many other factors. If your results are different from the results suggested below, this may not mean that you have a disease. Contact your healthcare worker if you have any questions. The following is considered to be a normal result for this test:
What follow up should I do after this test?
Ask your healthcare worker how you will be informed of the test results. You may be asked to call for results, schedule an appointment to discuss results, or notified of results by mail. Follow up care varies depending on many factors related to your test. Sometimes there is no follow up after you have been notified of test results. At other times follow up may be suggested or necessary. Some examples of follow up care include changes to medication or treatment plans, referral to a specialist, more or less frequent monitoring, and additional tests or procedures. Talk with your healthcare worker about any concerns or questions you have regarding follow up care or instructions.
If you have a positive urethral culture, you may need to have the test repeated to monitor the treatment of your diagnosed condition. Additionally, all of your sexual partners may need to be treated. Follow the instructions given to you by your healthcare worker regarding sexual activities.
Where can I get more information?
- Centers for Disease Control and Prevention (CDC) - http://www.cdc.gov/
- American Social Health Association (ASHA) - http://www.ashastd.org
 Cook RL, Hutchison SL, Ostergaard L, et al: Systematic review: noninvasive testing for Chlamydia trachomatis and Neisseria gonorrhoeae. Ann Intern Med 2005; 142(11):914-925.
 Shrier LA, Dean D, Klein E, et al: Limitations of screening tests for the detection of Chlamydia trachomatis in asymptomatic adolescent and young adult women. Am J Obstet Gynecol 2004; 190:654-662.
 Johnson RE, Newhall WJ, Papp JR, et al: Screening tests to detect Chlamydia trachomatis and Neisseria gonorrhoeae infections--2002. MMWR Recomm Rep 2002; 51(RR-15):1-38.
Last Updated: 6/4/2018