Type of test Blood
Normal findings
Negative or nonreactive
Test explanation and related physiology
Serologic tests are used to diagnose and to document successful therapy for syphilis. Syphilis is caused by the spirochete Treponema pallidum that cannot be isolated in culture. Two groups of antibodies form the basis for these tests. The first and older of these tests detects a nontreponemal antibody called reagin, which reacts to phospholipids similar to lipids in the membrane of T. pallidum. The nontreponemal antibody tests are relatively nonspecific and lack sensitivity. These antibodies would be detected by the Wassermann test, VDRL test, or RPR test. These test results become positive after 2 weeks from the patient’s inoculation with T. pallidum and return to normal after adequate treatment is administered. The test result is positive in nearly all primary and secondary stages of syphilis and in two-thirds of patients with tertiary syphilis. Screening for syphilis is usually done during the first prenatal checkup for pregnant women using the VDRL or RPR. VDRL is the only test that can be used on cerebral spinal fluid (CSF) when evaluating neuro syphilis. They are also used to document the success of treatment.
If these nontreponemal serologic test results are positive, the diagnosis must be confirmed by the second type of syphilis test, called Treponema test, such as the FTA absorption test (FTA-ABS) or the microhemagglutination assay (MHA-TP). These tests for a more specific antibody are more accurate than the VDRL and RPR tests. The FTA-ABS and MHA-TP are technically simple to perform, but they are labor intensive and require subjective interpretation by testing personnel. In contrast, the syphilis IgG enzyme immunoassay (EIA) is a treponemal test for the detection of IgG class antibodies.
During early primary syphilis, the first antibodies to appear are IgM, with IgG antibodies reaching significant titers later in the primary phase. As the disease progresses into the secondary phase, IgG T. pallidum antibodies reach peak titers. T. pallidum IgG antibodies persist indefinitely, regardless of the course of the disease. If syphilis IgG and/or IgM is positive, results can be confirmed with FTA or MHA testing. The IgG- and IgM specific antibodies assist in determining the etiology of neonatal syphilis. IgM does not pass through the placenta and, if positive, indicates active neonatal infection.
Interfering factors
• Excessive hemolysis and gross lipemia may affect test results.
• Excess chyle in the blood may interfere with the test results.
• Many conditions cause false-positive results when VDRL and RPR tests are used. Some of these conditions include Mycoplasma pneumonia, malaria, acute bacterial and viral infections, autoimmune diseases, and pregnancy.
• Recent ingestion of alcohol may alter the test results.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: verify with laboratory
• Blood tube commonly used: red
• Check with the laboratory regarding fasting requirements. Some prefer collecting the specimen before meals. Some lab oratories request that the patient refrain from alcohol for 24 hours before the blood test.
* If the test result is positive, instruct the patient to inform recent sexual contacts so that they can be evaluated.
* If the test result is positive, be sure the patient receives the appropriate antibiotic therapy.
Abnormal findings
- Syphilis
