T. pallidum cannot be visualized by light microscopy but can be seen using darkfield microscopy.

Serologic testing is an indirect method of diagnosis since it relies upon a maternal humoral immune response to the infection.

Two types of serologic testing are available:

Nontreponemal Antibody tests (Venereal Disease Research Laboratory(VDRL) and the Rapid Plasma Reagin (RPR)- are performed on serum and used as the screening tests for syphilis.

Treponemal Antibody tests (Fluorescent Treponemal Antibody Absorption (FTA-ABS) and microhemagglutination test for antibodies to T. pallidum (MHA-TP) are confirmatory tests that detect antibodies specifically directed at treponemal cellular components.