Diagnosis

If your sexual history and current signs and symptoms suggest that you have an STI, laboratory tests can identify the cause and detect coinfections you might have contracted.

  • Blood tests. Blood tests can confirm the diagnosis of HIV or later stages of syphilis.
  • Urine samples. Some STIs can be confirmed with a urine sample.
  • Fluid samples. If you have active genital sores, testing fluid and samples from the sores may be done to diagnose the type of infection. Laboratory tests of material from a genital sore or discharge are used to diagnose some STIs.

Screening

Testing for a disease in someone who doesn't have symptoms is called screening. Most of the time, STI screening is not a routine part of health care, but there are exceptions:

  • Everyone. The one STI screening test suggested for everyone ages 13 to 64 is a blood or saliva test for human immunodeficiency virus (HIV), the virus that causes AIDS.
  • Everyone born between 1945 and 1965. There's a high incidence of hepatitis C in people born between 1945 and 1965. Since the disease often causes no symptoms until it's advanced, experts recommend that everyone in that age group be screened for hepatitis C.
  • Pregnant women. Screening for HIV, hepatitis B, chlamydia and syphilis generally takes place at the first prenatal visit for all pregnant women. Gonorrhea and hepatitis C screening tests are recommended at least once during pregnancy for women at high risk of these infections.
  • Women age 21 and older. The Pap test screens for cervical abnormalities, including inflammation, precancerous changes and cancer, which is often caused by certain strains of human papillomavirus (HPV). Experts recommend that starting at age 21, women should have a Pap test at least every three years. After age 30, women are advised to have an HPV DNA test and a Pap test every five years or a Pap test every three years.
  • Women under age 25 who are sexually active. All sexually active women under age 25 should be tested for chlamydia infection. The chlamydia test uses a sample of urine or vaginal fluid you can collect yourself. Some experts recommend repeating the chlamydia test three months after you've had a positive test and been treated.

    The second test is needed to confirm that the infection is cured as reinfection by an untreated or undertreated partner is common. A bout of chlamydia doesn't protect you from future exposures. You can catch the infection again and again, so get retested if you have a new partner.

    Screening for gonorrhea also is recommended in sexually active women under age 25.

  • Men who have sex with men. Compared with other groups, men who have sex with men run a higher risk of acquiring STIs. Many public health groups recommend annual or more frequent STI screening for these men. Regular tests for HIV, syphilis, chlamydia and gonorrhea are particularly important. Evaluation for hepatitis B also may be recommended.
  • People with HIV. If you have HIV, it dramatically raises your risk of catching other STIs. Experts recommend immediate testing for syphilis, gonorrhea, chlamydia and herpes after being diagnosed with HIV. People with HIV should also be screened for hepatitis C.

    Women with HIV may develop aggressive cervical cancer, so they should have a Pap test within a year of being diagnosed with HIV, and then again six months later.

  • People who have a new partner. Before having vaginal or anal intercourse with new partners, be sure you've both been tested for STIs. Keep in mind that human papillomavirus (HPV) screening isn't available for men. No good screening test exists for genital herpes for either sex, so you may not be aware you're infected until you have symptoms.

    It's also possible to be infected with an STI yet still test negative, particularly if you've recently been infected.