Which test best confirms cat-scratch fever by detecting serum antibodies?

Which test best confirms cat-scratch fever by detecting serum antibodies?

• A. CBC
• B. CRP
• C. IFA
• D. Blood culture

Answer: (C)

Serum antibody testing against Bartonella henselae is the best way to confirm cat-scratch fever because the organism is difficult to culture and serology directly demonstrates the immune response to the infection. The indirect immunofluorescent assay uses Bartonella antigen on a slide, adds the patient’s serum, and then uses a fluorescently labeled anti-human antibody to detect any antibodies bound to the antigen. A positive result supports the diagnosis in the right clinical context of cat exposure and regional lymphadenopathy. In contrast, a CBC or CRP only show nonspecific inflammation, and blood cultures are often negative because Bartonella is fastidious and difficult to grow, making culture unreliable for confirmation.

Serum antibody testing against Bartonella henselae is the best way to confirm cat-scratch fever because the organism is difficult to culture and serology directly demonstrates the immune response to the infection. The indirect immunofluorescent assay uses Bartonella antigen on a slide, adds the patient’s serum, and then uses a fluorescently labeled anti-human antibody to detect any antibodies bound to the antigen. A positive result supports the diagnosis in the right clinical context of cat exposure and regional lymphadenopathy. In contrast, a CBC or CRP only show nonspecific inflammation, and blood cultures are often negative because Bartonella is fastidious and difficult to grow, making culture unreliable for confirmation.