Diagnosis

If your sexual history and current signs and symptoms suggest that you have a sexually transmitted disease (STD) or a sexually transmitted infection (STI), your doctor will do a physical or pelvic exam to look for signs of infection, such as a rash, warts or discharge.

Tests

Laboratory tests can identify the cause and detect coinfections you might also have.

• 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 open genital sores, your doctor may test fluid and samples from the sores to diagnose the type of infection.

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. Screening is recommended for:

• 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. Experts recommend that people at high risk have an HIV test every year.
• 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. All pregnant women will generally be screened for HIV, hepatitis B, chlamydia and syphilis at their first prenatal visit. 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 changes in the cells of the cervix, including inflammation, precancerous changes and cancer. Cervical cancer is often caused by certain strains of HPV.

  Experts recommend that women have a Pap test every three years starting at age 21. After age 30, experts recommend women have an HPV test and a Pap test every five years. Or, women over 30 could have a Pap test alone every three years or an HPV test alone every three years.

• Women under age 25 who are sexually active. Experts recommend that all sexually active women under age 25 be tested for chlamydia infection. The chlamydia test uses a sample of urine or vaginal fluid you can collect yourself.

  Reinfection by an untreated or undertreated partner is common, so you need the second test to confirm that the infection is cured. You can catch chlamydia multiple times, so get retested if you have a new partner.

  Screening for gonorrhea is also 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. They also recommend that people with HIV be screened for hepatitis C.

  Women with HIV may develop aggressive cervical cancer, so experts recommend they have a Pap test at the time of the HIV diagnosis or within a year of becoming sexually active if they are under 21 and have HIV. Then, experts recommend repeating the Pap test every year for three years. After three negative tests, women with HIV can get a Pap test every three years.

• People who have a new partner. Before having vaginal or anal intercourse with new partners, be sure you've both been tested for STIs. However, routine testing for genital herpes isn't recommended unless you have symptoms.

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