Syphilis tests detect antibodies to the bacterium that causes syphilis (Treponema pallidum) in blood, body fluid, or tissue. The tests are used to screen for or to confirm a syphilis infection.
Syphilis is a sexually transmitted infection (STI) that is usually spread during sexual contact, including kissing or oral sex.
Tests used to screen for syphilis include:
- Venereal disease research laboratory (VDRL) test. The VDRL test checks for an antibody that can be produced in people who have syphilis. This antibody is not produced as a reaction to the syphilis bacteria specifically, so this test is sometimes not accurate. The VDRL test may be done on a sample of blood or spinal fluid. The VDRL test is not very useful for detecting syphilis in very early or advanced stages.
- Rapid plasma reagin (RPR) test. The RPR test also detects syphilis antibodies.
- Enzyme immunoassay (EIA) test. This is a newer blood test that checks for antibodies to the bacteria that cause syphilis. A positive EIA test should be confirmed with either the VDRL or RPR tests.
Tests used to diagnose syphilis include:
- Fluorescent treponemal antibody absorption (FTA-ABS) test. The FTA-ABS test checks for antibodies to the bacteria that cause syphilis and can be used to detect syphilis except during the first 3 to 4 weeks after exposure to syphilis bacteria. The test can be done on a sample of blood or spinal fluid.
- Treponema pallidum particle agglutination assay (TPPA). The TPPA test is used to confirm a syphilis infection after another method tests positive for the syphilis bacteria. This test detects antibodies to the bacteria that cause syphilis. This test is not done on spinal fluid.
- Darkfield microscopy. This test uses a special microscope to examine a sample of fluid or tissue from an open sore (chancre) for the syphilis bacteria. This test is used mainly to diagnose syphilis in an early stage.
- Microhemagglutination assay (MHA-TP). The MHA-TP is used to confirm a syphilis infection after another method tests positive for the syphilis bacteria.
Why It Is Done
A syphilis infection can spread through the bloodstream to all parts of the body. If not treated, syphilis can cause severe heart disease, brain damage, spinal cord damage, blindness, and death.
A test for syphilis is done to:
- Screen for syphilis or check treatment for a syphilis infection. Screening tests help your doctor look for a certain disease or condition before any symptoms appear. This increases the chance of finding the infection when it can be cured or treated to avoid long-term problems.
- Some states require the VDRL screening test before a couple can obtain a marriage license.
- The Centers for Disease Control and Prevention (CDC) and the U.S. Preventive Services Task Force (USPSTF) recommend that all pregnant women be screened for syphilis early in pregnancy.1, 2
- Confirm that a syphilis infection is present.
Screening for syphilis and other sexually transmitted infections (STIs) is often done for people who engage in high-risk sexual behavior. If you have syphilis, your sex partner or partners should be notified, tested, and treated to prevent serious complications and to stop the spread of the disease.
How To Prepare
Tell your doctor if you:
- Are taking any medicines, such as antibiotics.
- Are allergic to any medicines, especially antibiotics, or medicine used to numb the skin (anesthetics).
- Have had bleeding problems or take blood-thinners, such as aspirin or warfarin (Coumadin).
- Are or might be pregnant.
If you have syphilis, do not have sex until the test results show you are no longer infected or until you and your sex partner or partners have completed treatment and the infection has been cured. Your sex partners should be tested as well.
If you think you might have syphilis, do not have sex until testing shows that you are not infected.
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results may mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).
How It Is Done
A syphilis test may be done on a sample of blood, sore, skin, or spinal fluid, depending on which type of test is done.
The health professional taking a sample of your blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol. Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood. Remove the band from your arm when enough blood is collected.
- Put a gauze pad or cotton ball over the needle site as the needle is removed.
- Put pressure on the site and then put on a bandage.
Sore or skin sample
A sample of fluid or tissue may be taken from an open sore (chancre) or from a rash that might be caused by syphilis.
- A fluid sample is obtained by gently pressing the chancre.
- Skin or mucous membrane samples may be obtained by gently rubbing a cotton-tipped swab over the area affected.
Fluid from a sore that may be caused by syphilis sometimes is collected and examined with a special type of microscope (darkfield microscope).
Spinal fluid sample
A spinal tap (lumbar puncture) is done to collect a spinal fluid sample for syphilis testing.
For a lumbar puncture, a thin needle is inserted into the spinal canal in the lower back area. After the needle is in place, a small amount of cerebrospinal fluid (CSF) is removed from the spinal canal. To learn more, see the topic Lumbar Puncture.
How It Feels
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
Sore or skin sample
You may have some discomfort when fluid is collected from an open sore (chancre). But chancres usually are not very tender or painful.
Spinal fluid sample
You may have some discomfort during a lumbar puncture to collect spinal fluid for syphilis testing. To learn more, see the topic Lumbar Puncture.
There is very little chance of a problem from having a blood sample taken from a vein.
- You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
- In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
- Ongoing bleeding can be a problem for people who have bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.
Sore or skin sample
There is very little risk of complications from having a sample taken from an open sore (chancre), skin rash, or mucous membrane.
Spinal fluid sample
There is little risk associated with having a lumbar puncture to obtain a spinal fluid sample for syphilis testing. To learn more, see the topic Lumbar Puncture.
Syphilis tests detect antibodies in blood or body fluid or tissue to the bacterium that causes syphilis (Treponema pallidum). Results are usually available in 7 to 10 days.
Darkfield microscopic examination
No syphilis bacteria are seen.
Syphilis bacteria are seen.
Syphilis tests of blood and spinal fluid
No antibodies to syphilis are present. This is called a nonreactive or negative result.
Antibodies to syphilis bacteria are present. This is called a reactive or positive test.
A result that is not clearly normal or abnormal is called inconclusive or equivocal.
Venereal disease research laboratory (VDRL) and rapid plasma reagin (RPR) tests
The antibody to the syphilis bacteria (reagin) is not present. This is called a nonreactive or negative result.
The antibody reagin is present. This is called a reactive or positive test.
The accuracy of testing often depends on the stage of syphilis. Syphilis testing may need to be repeated if initial results are uncertain or if you have had repeated exposure to syphilis, such as from repeated unprotected intercourse.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
- The use of antibiotics before having the test.
- A blood transfusion in the weeks before having the test.
- Having other conditions or diseases, such as lupus, liver disease, HIV infection, or a tropical bacterial infection called yaws.
What To Think About
Most states require doctors to report all cases of syphilis to the local health department. In some states, doctors are also required to ask for the names and addresses of your recent sex partners. If you have syphilis, the health department may contact you to make sure that you get treatment. If you give the names of your sex partners to your doctor or the health department, they will be contacted in confidence by the health department and advised to have a test for syphilis.
- If a screening test is positive (reactive), the strength of the result may be determined by measuring the amount of reagin. The results are then given in titers.
- A reactive or positive test result does not always mean that you have syphilis. Other conditions can cause positive screening test results, including injecting illegal drugs, recent vaccinations, endocarditis, autoimmune diseases (such as systemic lupus erythematosus, or SLE), tuberculosis, mononucleosis, leprosy, malaria, hepatitis, Lyme disease, rheumatoid arthritis, and in rare cases, pregnancy.
- With treatment, a positive reagin (VDRL and RPR) syphilis test result usually becomes negative. Positive treponemal (FTA-ABS, MHA-TP, TPPA) tests stay positive for a lifetime.
Syphilis and HIV infection
- Sores caused by syphilis (chancres) make it easier to get and spread an HIV infection.
- People with HIV infection who have a negative VDRL test should have a second test for syphilis if the infection is suspected.
Centers for Disease Control and Prevention (2010). Syphilis section of Sexually transmitted diseases treatment guidelines, 2010. MMWR, 59(RR-12): 26-39. Also available online: http://www.cdc.gov/std/treatment/2010/default.htm.
U.S. Preventive Services Task Force (2009). Screening for syphilis infection in pregnancy: U.S. Preventive Services Task Force reaffirmation recommendation statement. Annals of Internal Medicine, 150(10): 705–709.
Other Works Consulted
Chernecky CC, Berger BJ (2013). Laboratory Tests and Diagnostic Procedures, 6th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
|Primary Medical Reviewer||Sarah Marshall, MD - Family Medicine|
|Specialist Medical Reviewer||Devika Singh, MD, MPH - Infectious Disease|
|Last Revised||September 29, 2011|