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.