If your doctor suspects that you may be infected with an STD, he or she will ask how many sexual partners you have had and if any of them have had an STD.
Then, your doctor will examine you, focusing on your genital area. He or she also will examine your anal area and in women, do a pelvic exam. In addition, your doctor may swab the tip of the penis in men, take a sample of any cervical discharge in women or take a sample from the rectum. The specimens are sent to a laboratory for testing. Similar measures may be done with any visible sores.
Your doctor may make a preliminary diagnosis based on the results of your physical examination. For example, painful sores would suggest genital herpes, whereas painless ulcers may indicate syphilis. In this way, you can begin treatment for your infection as soon as possible, even before results of laboratory tests are available.
Different tests will be done depending on your symptoms. In the case of genital herpes, if you have an ulcer, it might be swabbed and tested in the lab. Blood tests can also be done to see if you have antibodies (infection-fighting proteins) against the herpes virus, which would indicate that you have been infected at some time in the past.
To test for chlamydia infections, your doctor will send a sample of fluid from the tip of the penis or cervix. Chlamydia can also be diagnosed with a urine test.
Gonorrhea requires a direct sample from the tip of the penis, cervix or rectum. Syphilis and HIV can be confirmed with a blood test. If you have an ulcer from syphilis, the diagnosis can be confirmed by looking at fluid from the ulcer under a special darkfield microscope to see if the bacteria are present.
If you have one STD, your doctor probably will recommend that you get tested for HIV and other STDs, because the risk factors are similar. Also, you are more likely to get HIV if you are infected with another STD.