The test is used to diagnose infection with syphilis in sexually active persons. Pregnant women also are screened, and many states in the U.S. require a blood test for syphilis when applying for a marriage license to prevent the spread of infection to others, especially a newborn baby.

A doctor may order the test:

• if you have symptoms, such as a chancre (sore) on the genitals or throat;
• if you are being treated for another sexually transmitted disease, such as gonorrhea;
• if you are pregnant, because untreated syphilis can infect and even kill a developing fetus; or
• if you complain of non-specific symptoms that resemble those of syphilis, to determine the exact cause of your illness.

If a scraping reveals presence of the syphilis bacterium (a positive test), you have an infection that requires treatment with a course of antibiotics.

The blood test detects the antibodies that the body produces to combat infection, so a positive test indicates that you have either a current or past infection. The blood test might not find antibodies for up to three months after exposure to the bacteria. In addition, the antibodies remain in the body for years, so if you have had a past infection with syphilis and were treated, your test results could still be positive. Therefore, to avoid being retreated, keep a record of the previous treatment and show it to your doctor.

Screening tests for syphilis are not highly specific and may give a false positive result. Positive tests should be confirmed with a more specific test method.

If you are sexually active, you should consult your doctor about any suspicious rash or sore in the genital area.

If you are infected, tell your sexual partner(s) to get tested and treated.

If you are infected, your risk of contracting other sexually transmitted diseases increases, including the risk of being infected with HIV, the virus that causes AIDS.