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Syphilis Tests

Test Overview

Syphilis tests tell if a person has this disease. They look for antibodies to the bacterium, or germ, that causes syphilis. Some tests look for the syphilis germ itself.

Syphilis is a sexually transmitted infection. That means it is spread through sexual contact: vaginal, anal, or oral sex.

Testing is done on blood, body fluid, or tissue samples.

If a first screening test shows signs of syphilis, another test is done to confirm a syphilis infection.

Screening tests

Tests used to screen for syphilis include:

  • Venereal disease research laboratory (VDRL) test. The VDRL test checks blood or spinal fluid for an antibody that can be produced in people who have syphilis. This antibody is not produced as a reaction to syphilis specifically, so the test result could be "abnormal" for reasons other than syphilis.
  • Rapid plasma reagin (RPR) test. The RPR test also finds syphilis antibodies.
  • Rapid immunochromatographic test. This test checks for antibodies that are specific to syphilis. Unlike other tests, the blood sample is not sent to a laboratory. You can find out the results at your doctor visit.

Tests to confirm syphilis

Tests used to confirm a syphilis infection include:

  • Enzyme immunoassay (EIA) test. This blood test checks for syphilis antibodies. A positive EIA test should be confirmed with either the VDRL or RPR tests.
  • Fluorescent treponemal antibody absorption (FTA-ABS) test. This test also checks for antibodies. It can be used to find syphilis except during the first 3 to 4 weeks after exposure. The test can be done on a sample of blood or spinal fluid.
  • Treponema pallidum particle agglutination assay (TPPA). This test also checks for antibodies. It is used after another method tests positive for syphilis. This test is not done on spinal fluid.
  • Darkfield microscopy. This test uses a special microscope to look for the syphilis germ in a sample of fluid or tissue from an open sore. 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 test shows positive results for syphilis.

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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.

Screening for syphilis and other sexually transmitted infections is often done for people who engage in sexual behaviors that put them at risk. A test for syphilis is done to:

  • Screen for syphilis. 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.
  • Check pregnant women for syphilis. Syphilis during pregnancy can cause very serious problems.
  • Confirm that a person has syphilis.
  • Check how well treatment is working.

If you have syphilis, your sex partner or partners should be told, tested, and treated to prevent serious problems and to stop the spread of the disease.

Learn more

How To Prepare

If you think you might have syphilis, do not have sex until testing shows that you are not infected.

If you have syphilis and are being re-tested, do not have sex until the test results show that 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.

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.

Blood test from a finger stick

For a finger-stick sample, the health professional will puncture the skin on your middle or ring finger with a small instrument called a lancet. Then they'll collect a small amount of blood.

Blood test from a vein

A health professional uses a needle to take a blood sample, usually from the arm.

Sore or skin sample

A sample of fluid or tissue may be taken from an open sore or from a rash that might be caused by syphilis.

  • A fluid sample is obtained by gently pressing the sore.
  • Skin or mucous membrane samples may be obtained by gently rubbing a cotton-tipped swab over the area.

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. After the needle is in place, a small amount of fluid is removed from the spinal canal.

How It Feels

Blood sample

When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.

Sore or skin sample

You may feel some discomfort when fluid is collected from an open sore. But syphilis sores usually aren't very tender or painful.

Spinal fluid sample

You may feel some discomfort during a lumbar puncture to collect spinal fluid.

Risks

Blood sample

There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.

Sore or skin sample

There is very little risk of problems from having a sample taken from an open sore, skin rash, or mucous membrane.

Spinal fluid sample

There is little risk linked with having a lumbar puncture to obtain a spinal fluid sample.

Results

Results are usually available in 7 to 10 days.

Darkfield microscopic examination

Normal:

No syphilis germs are seen.

Abnormal:

Syphilis germs are seen.

Syphilis tests of blood and spinal fluid

Normal:

No syphilis antibodies are found. This is called a nonreactive or negative result.

Abnormal:

Antibodies are found. 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

Normal:

Syphilis antibodies are not found. This is called a nonreactive or negative result.

Abnormal:

Antibodies are found. This is called a reactive or positive test.

A reactive or positive test result does not always mean that you have syphilis. Other conditions can cause positive test results. These include injecting illegal drugs, recent vaccinations, endocarditis, and autoimmune diseases.

The accuracy of testing often depends on the stage of syphilis. Testing may need to be repeated if:

  • Results of the first test are uncertain.
  • You have had repeated exposure to syphilis, such as from repeated unprotected intercourse.

Credits

Current as of: February 11, 2021

Author: Healthwise Staff
Medical Review:
Kathleen Romito MD - Family Medicine
E. Gregory Thompson MD - Internal Medicine
Martin J. Gabica MD - Family Medicine
Adam Husney MD - Family Medicine
Kevin C. Kiley MD - Obstetrics and Gynecology