In the bad old days, men who thought they might have chlamydia or gonorrhea got tested by having a swab inserted into their urethra, and women had to undergo a pelvic exam. Fortunately, thanks to technology, both of these STDs can now be detected via urine testing. Urine chlamydia tests and gonorrhea tests are a heck of a lot more pleasant than urethral swabs, although in some places urine testing can be difficult to find.
The gold standard for diagnosing bacterial STDs, such as chlamydia and gonorrhea, is still direct testing of specimens from the cervix or urethra using bacterial culture, which attempts to grow any bacteria that might be present in the sample. However, most urine testing work by looking for bacterial DNA using a process called LCR (ligase chain reaction) or other DNA amplification techniques. These types of testing are sensitive to even very small amounts of bacterial DNA and do not require a live bacterial sample.
The debate over whether urine testing is as effective at detecting chlamydia and gonorrhea as is testing of cervical and urethral swabs often focuses on women, because the most common site of female infection (the cervix) is not on the pathway that urine travels out of the body. However, worries about urine testing efficacy seem to be reasonably unfounded.
The science suggests that although urine testing may not pick up quite as many cases as swab testing, it will still identify most infected individuals. That is great news for people who want to be tested for gonorrhea and chlamydia - the two most common curable STDs - in a less invasive way, although some other STD tests still do require either a physical examination or a blood draw.
How comparable are swab testing and urine testing for gonorrhea and chlamydia?
A 2005 study that examined 29 studies of the relative effectiveness of urine testing compared to swab testing using three different amplification techniques (PCR, transcription-mediated amplification, and strand-displacement amplification) found that:
- For chlamydia testing in women, the sensitivity and specificity were 80-90 percent and 98-99 percent for urine samples and 85-98 percent and 98-99 percent for cervical samples.
- For chlamydia testing in men, the sensitivity and specificity were 84-93 percent and 93-99 percent for urine samples and 87-95 percent and 96-99 percent for urethral samples.
- For gonorrhea testing in women, the sensitivity and specificity were 55-91 percent and 98-99 percent for urine samples and 94-99 percent and 99 percent for cervical samples.
- For gonorrhea testing in men, the sensitivity and specificity were 90 percent and 99 percent for urine samples and 96 percent and 99 percent for urethral samples.
To sum up, although cervical and urethral testing were slightly more effective than urine testing for chlamydia and gonorrhea, gonorrhea and chlamydia urine tests were more than good enough in most circumstances.
Cook, R.L. et al. (2005) "Systematic Review: Noninvasive Testing for Chlamydia trachomatis and Neisseria gonorrhoeae" Ann Intern Med. 142:914-925.