VDRL

The VDRL test is a useful screening test for syphilis and is positive within 3 - 4 weeks after primary infection; generally it becomes negative 6 months after treatment. The basis of the test is that an antibody produced by a patient with syphilis reacts with an extract of ox heart (diphosphatidyl glycerol). The antibody is detected by a flocculation reaction.

Note that this test may also be negative in untreated patients - 50% with late stage syphilis.

Although it is not specific for syphilis, titres are useful in analysis of disease activity and in screening:

• a falling titre indicates successful treatment.
• a rising titre indicates treatment failure or reinfection