The role of the laboratory in assisting treatment--a review of current UK practices.

A questionnaire concerning the laboratory management of endocarditis was sent to 120 UK microbiologists. The 86 replies received indicated that most microbiologists undertake in-vitro sensitivity tests on both streptococci and staphylococci and nearly all perform serum bactericidal titres. Neither the methods used for these investigations nor the interpretation of the results obtained are uniform. Considerable importance is attached to the serum bactericidal titres and many microbiologists alter the antibiotic regimen on the basis of unsatisfactory results. The serum bactericidal titre obtained in 114 patients with endocarditis seen at St. Thomas' Hospital between 1970 and 1985 were analysed according to the outcome of the infection; this was classified as (i) cure, (ii) bacteriological cure/clinical failure or (iii) failure. There were only six failures, four of which had peak titres less than 1:8. Trough titres were of no predictive value. Peak titres of greater than 1:8 were reasonably predictive of bacteriological cure but not of clinical outcome. Failure of medical treatment in endocarditis is seldom the result of inappropriate antibiotics, it usually results from late diagnosis or late referral to cardiologists and cardiac surgeons. Critical evaluation of serum bactericidal titres is long overdue.