Syphilis is a sexually transmitted disease (STD) caused by a certain type of bacteria (called Treponema pallidum). This type of bacteria  is usually spread during sexual contact (including kissing or oral sex).

A syphilis infection can spread through the bloodstream to all parts of the body. If not treated, syphilis can progress through three stages, usually extending over many years, to the point of affecting behavior. A syphilis test may be done for evaluating people with symptoms of dementia. The last stage of the disease can cause severe heart disease, brain damage, spinal cord damage, blindness, and death.

A pregnant woman with untreated syphilis can pass the infection to her fetus during pregnancy or birth (congenital syphilis). The risk of infecting the fetus is greatest when the mother is in the early stages of syphilis. However, fetal infection is possible any time during pregnancy when the mother is infected with syphilis.

If the pregnant woman receives treatment before the 16th week of pregnancy, the newborn usually will not have any signs of the illness and will not have syphilis in his or her blood. Untreated infection during pregnancy can cause miscarriage, premature birth, stillbirth, or birth defects in the fetus.

There are several methods used to test for syphilis:

• Venereal disease research laboratory (VDRL) test. The VDRL test is done to screen for syphilis. It checks for an antibody called reagin that can be produced in people who have syphilis. Reagin is not produced as a reaction to the syphilis bacteria specifically, so sometimes this test  can be inaccurate. 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 reagin and is commonly used as a screening test. The RPR test is done on a sample of blood. It is not done on spinal fluid.
• Fluorescent treponemal antibody absorption (FTA-ABS) test. The FTA-ABS test is more difficult to do and is not used as a screening test. It may be used to confirm a syphilis infection after a positive screening test. This test detects antibodies to the bacteria that cause syphilis and can be used to detect syphilis in all stages (except for the first 3 to 4 weeks). The test can be done on a sample of blood or spinal fluid.
• Microhemagglutination assay (MHA-TP). The microhemagglutination assay for Treponema pallidum (MHA-TP) is used to confirm a syphilis infection after screening test results indicate syphilis. The MHA-TP test detects antibodies to the bacteria that cause syphilis and can be used to detect syphilis in all stages (except for the first 3 to 4 weeks). This test is not done on spinal fluid.

Syphilis Tests
Results

Results of syphilis testing are usually reported as:

• Nonreactive or negative if syphilis is not detected. These are normal results.
• Reactive or positive if syphilis is detected. These are abnormal results. It takes about 4 to 6 weeks after exposure to syphilis for a blood test to be positive.
• Reactive equivocal or inconclusive if the results are not clear. These are not clearly normal or abnormal results.

A screening test (VDRL or RPR test) only detects the presence or absence of reagin. 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 titer is a measure of how much the blood or spinal fluid sample can be diluted before the reagin can no longer be detected.

A titer of 1 to 20 (1:20) means that reagin can be detected when 1 part of the blood or spinal fluid sample is diluted by up to 20 parts of a salt solution (saline). A larger second number means there is more reagin in the sample. Therefore, a titer of 1 to 80 indicates more reagin than a titer of 1 to 20.

The accuracy of testing often depends upon the stage of syphilis. Syphilis testing may need to be repeated if initial results are uncertain or if there is repeated exposure to syphilis (such as from repeated unprotected intercourse).

A reactive or positive test result does not always indicate syphilis. This is especially true of the syphilis screening tests (VDRL and RPR tests). Many other conditions can cause positive test results, including chickenpox, tuberculosis, systemic lupus erythematosus (SLE), mononucleosis, leprosy, malaria, hepatitis, Lyme disease, and rheumatoid arthritis.