Serological investigations in the diagnosis and management of infective endocarditis.

In a retrospective study of 39 patients with infective endocarditis (IE) all had elevated concentrations of C reactive protein (CRP) at presentation, patients with the acute variety having significantly higher values than patients with the subacute variety. In addition, the majority of patients with subacute bacterial endocarditis had elevated concentrations of circulating immune complexes (CICs) and rheumatoid factor (RF), both of which were absent in all but one of nine patients with acute bacterial endocarditis. Two patients with subacute and one with acute bacterial endocarditis had low values of C3 and C4. Measurement of CRP, CICs, and RF did not distinguish between patients with and without extracardiac manifestations. Sequential analysis of patients revealed that a successful response to antimicrobial treatment was indicated by a striking and rapid decline in CRP, with less striking declines in CICs, RF, and IgM. Antibiotic failure was indicated by the persistence of high concentrations of CRP and CICs. We conclude that the measurement of C reactive protein is of some value in the diagnosis and management of infective endocarditis. A normal CRP concentration excludes this diagnosis. The measurement of CRP alone appears sufficient for monitoring most cases of infective endocarditis with the sequential measurement of rheumatoid factor and circulating immune complexes adding no useful information except where the CRP remains elevated despite treatment. In this latter instance, persisting high levels of CRP and circulating immune complexes together herald an ominous course.