Detection of antibody against cardiolipin is useful for the diagnosis of which disease?

• A. Leptospirosis
• B. Lyme disease
• C. Relapsing fever
• D. Syphilis

Answer: (D)

Antibodies against cardiolipin reflect a non-specific immune response produced during syphilis infection. Tests like VDRL and RPR use a cardiolipin-containing antigen (cardiolipin-lecithin-cholesterol) to detect these reagin antibodies in patient serum. Because these antibodies are not directed at the actual Treponema pallidum bacterium, the test is useful for screening and for monitoring disease activity and treatment response—the titers tend to be higher in active disease and fall after successful therapy. It’s not specific to syphilis, but in the context of these choices, the classic association is with syphilis. Other listed diseases are diagnosed using pathogenspecific methods (for example, Borrelia-specific tests for Lyme disease, serology orMAT for leptospirosis, and tests targeting relapsing fever organisms), not cardiolipin-based reagin tests.