What is the best way to diagnose primary syphilis?

Diagnosis cannot be based on clinical presentation alone, and, unfortunately, T. pallidum cannot be cultured. The most specific and rapid method of diagnosing primary syphilis is the demonstration of the spirochete utilizing darkfield examination by a trained observer. This test is not readily available to most community physicians and usually requires sending the patient to a sexually transmitted disease (STD) clinic or medical center. The material for examination can be obtained from either the ulcer or an aspirate from an enlarged lymph node. A single negative darkfield examination does not rule out the possibility of syphilis, and it should not be regarded as negative until there are negative examinations on 3 consecutive days. Primary syphilis can also be diagnosed by biopsying the primary ulcer and demonstrating the organism by special stain.


In lieu of these procedures, a presumptive diagnosis can be made by serologic tests (see Chapter 3). The Venereal Disease Research Laboratory (VDRL) test and rapid plasma reagin (RPR) test are negative in early primary syphilis and should be repeated weekly for 1 month to be considered as negative. The diagnosis is more likely if a rising titer can be demonstrated. The fluorescent treponemal antibody-absorption (FTA-ABS) test turns positive earlier and is more sensitive.