Laboratory aspects of infective endocarditis.

The clinical laboratory has a major role in both the diagnosis and treatment of cases of infective endocarditis. Patients often present with vague non-specific symptoms, which complicates the initial diagnosis. Blood cultures are by far the most important specimens. Laboratories should be aware of isolation problems associated with certain organisms. If initial blood cultures are negative then serological tests for non-bacterial causes should be considered. Staphylococci and streptococci account for > 90% of cases, and appropriate antimicrobial chemotherapy for the majority of strains is well established. The laboratory role is to identify the infecting organism, to establish the in-vitro activity of the proposed antibiotic therapy by determining minimum inhibitory concentrations and minimum bactericidal concentrations of antibiotics, singly and in combination against the patient's own organism, and to measure the bactericidal activity of antibiotics in the patient's serum to assess potential clinical efficacy. Laboratory aspects of diagnosis, treatment and therapeutic monitoring are discussed.