Interpretation of spectrophotometric absorbance values to define results of enzyme-linked immunosorbent assays.

An enzyme-linked immunosorbent assay method was used to classify bovine serum as positive, negative, or doubtful for antibodies to Brucella abortus. Spectrophotometric data from assays of 64 serologically positive and 32 serologically negative bovine sera were analyzed statistically to define the range of spectrophotometric absorbance values which classify sera. Statistical analysis indicated that absorbance values less than 0.08 should be considered negative and values greater than 0.14 should be considered positive, with intermediate values declared doubtful, and that the probability of erroneously classifying a positive serum as negative or a negative serum as positive is less than 0.005.