The World Health Organization estimated in 1999 that nearly one million people worldwide contracted a new sexually transmitted disease, or STD, every day. Doctors use several different tests to look for STDs based on the characteristics of the infection they are looking to detect. Anyone who has had one or more unprotected sexual encounters should consider being tested for STDs, even if she is asymptomatic.
Blood Tests
Blood tests are used to check for the presence of specific antibodies against human immunodeficiency virus, or HIV, that are produced when someone is infected. A positive antibody test needs to be confirmed with another more specific polymerase chain reaction, or PCR, test that detects HIV DNA.
Two other antibody tests called the rapid plasma regain, or RPR, and venereal disease research laboratory, or VDRL, look for antibodies that can be produced when a person has syphilis. These tests have a significant risk of being positive when there is no infection, so a confirmatory test such as the fluorescent treponemal antibody absorption test "FTA-Abs" should be done to check for syphilis-specific antibodies.
There are also PCR blood tests for herpes, but these can be negative when someone is actually infected.
Pap Smears
A pap smear involves taking a sample of cells from the opening of a women's cervix, also called the cervical os. The doctor will insert a speculum into the vagina. When the speculum is opened, it provides a view of the cervix, which lies between the vagina and the uterus. The doctor will place a small brush into the opening of the cervix and some of the woman's cervical cells will attach to the brush. The cells are then sent to a lab. In the lab, the cells are examined under the microscope for signs of the human papilloma virus, HPV.
Cultures
For gonorrhea and chlamydia, testing is traditionally done by taking a sample by placing a cotton swab inside the urethral meatus, the opening of the penis in men, or into the cervical opening in women. The material on the swab is then placed in special growth media that only allows certain bacteria to grow. These samples then undergo more tests to determine if the bacteria are chlamydia or gonorrhea.
Urine Sample
A newer way to test for gonorrhea and chlamydia uses a urine sample, which is much more convenient for patients. The test is positive if DNA for either type of bacteria is detected in the urine sample using a PCR technique.
Wet Mount
A wet mount is a test where some cells are scraped from the female cervical opening during the speculum exam and placed on a microscope slide along with some fluid. This process can detect Trichomonas vaginalis, which can be seen with a microscope.
This test is also used to look for non-sexually transmitted conditions like yeast infections and bacterial vaginosis.
Skin
For those STDs that manifest as a skin sore, a physician may scrape some cells from the edge of the sore to use for other tests. Syphilis organisms can be seen by looking under a special Darkfield microscope, and herpes can be detected by doing PCR on the sample. Chancroid is another STD producing a skin sore that is diagnosed based on symptoms and exam, no test is currently available.
References
- "Red Book: 2009 Report of the Committee on Infectious Diseases, 28th ed."; Human Immunodeficiency Virus Infection; LK Pickering, ed; 2009.
- "Red Book: 2009 Report of the Committee on Infectious Diseases, 28th ed."; Human Papillomaviruses; LK Pickering, ed; 2009.
- "Red Book: 2009 Report of the Committee on Infectious Diseases, 28th ed."; Gonoccocal Infections; LK Pickering, ed; 2009.
- "Infectious Disease Clinics of North America"; Rapid Diagnostic Methods in Sexually Transmitted Infections; Laura Greer, M.D. and George D. Wendel, Jr, M.D.; 2008.
