In nontreponemal tests for syphilis such as VDRL and RPR, the antigen consists of cardiolipin, lecithin and cholesterol. Which component serves as the principal antigenic determinant reacting with the patient's reagin antibodies?
- A Cardiolipin ✓
- B Lecithin
- C Cholesterol
- D Treponemal membrane protein added during preparation
Correct answer: A. Cardiolipin
Explanation
Cardiolipin, derived from beef heart, is the reactive component that combines with anticardiolipin reagin antibodies in the patient's serum to form visible floccules. Lecithin and cholesterol act as stabilizers that enhance flocculation sensitivity and reproducibility but are not themselves the antigen. No treponemal proteins are present in nontreponemal antigen, which is precisely why these tests screen rather than confirm syphilis.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.