Phospholipid used to investigate syphilis by the regain test is

Ans. a (Cardiolipin). (Ref. Ananthanarayan, Microbiology, 6th/pg.378; 7th ed. pg. 381)SEROLOGICAL TESTS FOR SYPHILISThese tests form the mainstay of laboratory' diagnosis.A Large number of tests have been described, of which only a few are now employed.These are follows:1. Tests for antibodies reacting with cardiolipin antigen (Non-specific reagin tests; standard tests for syphilis; STS)2. Tests for antibodies reacting with group specific treponemal antigen3. Tests for specific antibodies to pathogenic treponema (T. pallidum).Reagin antibody testsThese tests use the lipoid or cardiolipin antigens and are known as 'standard tests for syphilis' or STS.The first of the reagin antibody tests was the Wassermann complement fixation test (1906).It is no longer in use now.# The first flocculation test used widely was tube flocculation test of Kahn.# The Kahn test has been replaced by the simpler and more rapid VDRL test., which gives more quantitative result.# VDRL test can be used for testing CSF also, but not plasma. CSF need not be heated prior to test.# A number of modifications of the VDRL have been developed, of which the Rapid Plasma Reagin (RPR) test is the most popular.Sensitivity of Serodiagnostic Tests in Untreated SyphilisMean Percentage Positive (Range) at Indicated Stage of DiseaseTestPrimarySecondaryLatentTertiaryVDRL, RPR78 (74-87)10095 (88-100)71 (37-94)FTA-ABS84 (70-100)10010096TP-PA89100100NA