Variation in performance of the serum bactericidal test.

Questionnaires were sent to 37 diagnostic microbiology laboratories to assess their methods for performance of the serum bactericidal test. Of the 28 responding laboratories, 26 utilized the test, with considerable variation among methods. Culture and dilution media included Trypticase soy, Mueller-Hinton, brain heart infusion, Columbia broth, dextrose phosphate, and pooled human serum. Several different schemes for dilution of the test serum were employed, including both micro and macro methods. The greatest variation occurred in the size of the bacterial inoculum, with only eight laboratories having a method for standardization of the inoculum. Other differences included the time of incubation, the method of subculture, and determination of the bactericidal end point. These studies emphasize the need for assessment of the variables in the performance of this test and for the development of a standard method for diagnostic laboratories.