Detection of antibody against cardiolipin is useful for diagnosing which disease?

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

Answer: (D)

Antibody detection against cardiolipin is a hallmark of screening tests for syphilis. The immune system makes reagin antibodies that target a cardiolipin-containing antigen used in non-treponemal tests (such as the VDRL and RPR). These tests are sensitive and useful for identifying active infection and for monitoring treatment response, since titers tend to fall with effective therapy. However, they are not perfectly specific to syphilis, because anti-cardiolipin antibodies can appear in other conditions as well, so a positive result is usually confirmed with a treponemal-specific test (like FTA-ABS or TP-PA). In the context of the options given, this cardiolipin antibody detection is most associated with diagnosing syphilis.