Development and evaluation of an enzyme-linked immunosorbent assay for bovine antibody to Pasteurella haemolytica: constructing an enzyme-linked immunosorbent assay titer.

A 2-stage strategy was developed and evaluated for estimating serum antibody titer by use of ELISA and a series of dilutions. In stage 1, the linear response region and least-square estimate of the assay line slope were established from 9-point dilution assays. Provided that the reading was within the linear response region, this information was used in the stage-2 estimation of titer from a single absorbance reading. Operationally, 2 fixed dilutions were selected, one suitably low and one suitably high, to provide at least one reading within the linear region. The procedure should save considerable time when a large number of assays are to be performed. Stage 1 required approximately twenty 9-point assays, but all subsequent assays required only 2 fixed dilutions.