The lack of a method for demonstrating the presence of Treponema palli
dum by growth necessitates the use of alternative methods. Traditional
ly, these methods are divided into direct detection methods (animal in
oculation, dark-field microscopy, etc.) and serologic tests for the pr
esence of patient antibody against T. pallidum. Serologic methods are
further divided into two classes. One class, the nontreponemal tests,
detects antibodies to lipoidal antigens present in either the host or
T. pallidum; examples are the Venereal Disease Research Laboratory and
rapid plasma reagin card tests. Reactivity in these tests generally i
ndicates host tissue damage that may not be specific for syphilis. Bec
ause these tests are easy and inexpensive to perform, they are commonl
y used for screening, and with proper clinical signs they are suggesti
ve of syphilis. The other class of test, the treponemal tests, uses sp
ecific treponemal antigens. Confirmation of infection requires a react
ive treponemal test. Examples of the treponemal tests are the microhem
agglutination assay for antibodies to T. pallidum and the fluorescent
treponemal antibody absorption test These tests ave more expensive and
complicated to perform than the nontreponemal tests. On the horizon a
re a number of direct antigen, enzyme-linked immunosorbent assay, and
PCR techniques. Several of these techniques have shown promise in clin
ical trials for the diagnosis of congenital syphilis and neurosyphilis
that are presently difficult to diagnose.