VDRL test is a nonspecific flocculation test for Syphilis. VDRL test is easy to perform and inexpensive, so it is commonly used in the screening of population for Syphilis. Without some other evidence for the diagnosis of syphilis, a reactive nontreponemal test does not confirm Treponema pallidum infection.
Principle of VDRL Test:
Non-treponemal antigen (Cardiolipin-Cholesterol-Lecithin) is used to detect the presence of “reagin antibodies” in patient’s serum.
When the heat inactivated (to destroy complement) serum of patient is reacted with freshly prepared non-treponemal antigen, flocculation reaction (antigen and antibody complex are suspended) occurs. The flocculation can be observed by using Microscope with 10x objective and 10x eye piece.
Reactive VDRL test serum can be quantitated to obtain the titre of “reagin antibodies” by using serial double dilution method.
Result and Interpretation of VDRL test
VDRL test is positive in most cases of Primary Syphilis and are almost always positive in Secondary Syphilis. The titer of reagin antibodies decreases with effective treatment, so VDRL test can be used to determine the treatment response of Syphilis.
False positive VDRL test result
Reagin antibodies may be produced in response to nontreponemal diseases of an acute and chronic nature in which tissue damage occurs such as:
- Hepatitis B
- Infectious Mononucleosis
- Vrious autoimmune Diseases
False negative VDRL test can be seen because of Prozone phenomenon (No flocculation due to antibody excess). In that case test serum has to be diluted further to obtain zone of equivalence (where maximum flocculation of Ag-Ab occurs).