The selection of tests for syphilis is dictated by the clinical situation. If the patient has possible primary syphilis, a dark-field examination would be helpful, although it is becoming difficult to find laboratories with the necessary equipment and laboratorians with sufficient expertise. If the dark-field test result is negative or cannot be performed, an FTA-ABS test should be done. If the FTA-ABS result is nonreactive and clinical suspicion is strong, the physician, for practical purposes, has the option of treating the patient without a conclusive diagnosis or of repeating the FTA-ABS test in 2-3 weeks.

If the patient has confirmed early syphilis, an RPR result should nevertheless be obtained. If the RPR result is reactive, the degree of reactivity should be titered, since a falling titer after treatment is evidence that treatment was effective.

If the patient has possible, equivocal, or late syphilis, an FTA-ABS (or MHA) and STS test should be done. If the FTA-ABS (or MHA) test result is reactive (2+ or more), the diagnosis is probable syphilis. If the FTA-ABS (or MHA) test result is weakly reactive (borderline or 1+ reactive), the test should be repeated in 1 month. If it is still weakly reactive, the diagnosis is possible or probable syphilis, depending on the clinical picture. The RPR results are useful mainly as additional evidence in equivocal cases.

If a routing screening RPR result is found to be positive in a person with no history or clinical evidence of syphilis, a confirmatory test should be done. If the confirmatory test result is negative, the patient should be screened for diseases known to cause a high incidence of BFP reactions. In this respect, a weakly positive RPR result may be due only to an acute BFP etiology, and the RPR result should be negative in 2-3 months. If the confirmatory test result is positive, past or present syphilis is a strong probability. Nevertheless, since even the confirmatory tests may occasionally produce a false positive (or false negative) reaction, in certain patients it may be necessary to repeat the confirmatory test.