"The mainstay of syphilis diagnosis is still serological testing.

• In common use is the rapid plasma reagent card (RPR).

Positive and negative reactions are illustrated.

 A positive reaction needs further evaluation by the fluorescent treponema antibody (FTA) test, because the RPR is non-specific, and false positives are common.

In a large sexually transmitted disease clinic, initial diagnosis of primary syphilis can be made by darkfield microscopy of fluid from the edge of a chancre, which is usually teeming with spirochetes.

•  However, this test must be read rapidly (within seconds or minutes), because the spirochetes quickly dry and become immobile, making diagnosis difficult. Hence, this test is usually restricted to STD clinics or state health departments where large number of tests are performed. "

1999- KUMC Pathology and the University of Kansas, used with permission; courtesy of Dr. James Fishback, Department of Pathology, University of Kansas Medical Center.