Positive tests are considered to be presumptive evidence of syphilis. The titer will fall over 6-8 months if the disease is adequately treated. Due to the nonspecificity of the test, false positives (FP`s) may occur. However, all reactive sera are confirmed by performing an MHA-TP test. FP`s of less than 6 months duration occur with measles, chickenpox, viral pneumonia, upper respiratory infections, pregnancy, and after receipt of a smallpox vaccination. Usually reactivity disappears spontaneously within a few days or weeks. Chronic FP`s (over 6 months) can be associated with SLE, metastatic carcinoma, rheumatoid arthritis, serum protein abnormalities, rheumatoid factors, and narcotic addiction. Reactive tests due to related treponemal infections will also occur. A falsely negative test can sometimes be seen because of a prozone effect (1-2% of patients with secondary syphilis). In late syphilis, the RPR may be nonreactive in 20-30% of cases. In suspected cases of late syphilis, the MHA-TP should be requested.
Nontreponemal agglutination screening test
In untreated syphilis, reactive sera are found in the chancre stage, 70% after 1 week, and 90% after 3 weeks. In the secondary stage, the RPR should be reactive 100% of the time, decreasing to 90% in the tertiary stage. In the latent stage and a month to 2 years after successful treatment, the RPR may become nonreactive. The titer of antibody will vary from patient to patient; there is no direct relationship between the amount of reagin and the severity of disease. All specimens determined to be reactive will be confirmed by MHA-TP testing. Patients from whom reactive results are obtained are reported to the City of Chicago Board of Health. This is mandated by law.