How is it used?
The tests are used to screen for and diagnose infection with
Treponema pallidum, the that causes syphilis. Screening of all pregnant women is recommended by the US Preventive Services Task Force, preferably at the first prenatal visit. Many states require a blood test for syphilis when a couple is applying for a marriage license in order to help prevent the spread of the infection to others, especially a newborn baby.
There are several methods that can be used to test for syphilis. One method used in diagnosis of early cases involves looking for the bacterium in scrapings from the chancre using a special instrument called a dark-field microscope. Other methods require a blood sample in which can be detected. These include:
- For screening – VDRL which stands for “venereal disease research laboratory” test and rapid plasma reagin test (RPR)
- For diagnosis - fluorescent treponemal antibody absorption test (FTA-ABS) and Treponema pallidum particle agglutination assay (TPPA)
A method called microhemagglutination assay, MHA-TP, is rarely used any more.
Response to treatment can be determined with a follow-up RPR test, and the FTA-ABS test is used to confirm a positive VDRL or RPR screening test. In late or latent syphilis, may be obtained using a spinal tap and then tested in order to diagnose brain involvement (neurosyphilis).
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When is it ordered?
A doctor may order the test:
- if you have symptoms, such as a chancre 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 you are infected, you should have follow-up blood tests at 3, 6, 12, and 24 months to make sure the infection is gone following treatment.
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What does the test result mean?
If a scraping reveals presence of the syphilis (a positive test), you have an infection that requires treatment with a course of antibiotics, preferably penicillin.
For the blood tests that detect the that the body produces to combat infection, a positive test indicates that you have either a current or past infection. However, a negative test does not always mean that you do not have syphilis.
Antibodies may not be able to be detected for up to three months after exposure to the bacteria, and the antibodies remain in the body for years. If you have had a past infection with syphilis and were treated, your test results could still be positive. For example, a FTA-ABS test may remain positive for life even if you have been treated. To avoid being retreated, keep a record of the previous treatment and show it to your doctor. Following treatment, syphilis antibodies should be lower and can be monitored with the titered RPR test; if they remain the same or rise, you may have a persistent infection.
The different tests available to screen and diagnose syphilis vary in their accuracy depending on the stage of disease. For example, the VDRL and RPR tests have highest during the middle stages.
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Is there anything else I should know?
Screening tests for syphilis are not highly
specific and may give a
false positive result. For example, having
HIV,
Lyme disease, malaria,
lupus, or certain types of pneumonia may cause a false positive result on the VDRL and RPR tests. Positive tests should be confirmed with a more specific test method, such as FTA-ABS.
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. The chancres caused by syphilis make it easier to transmit and acquire HIV.
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