Agreement between three serological tests for Neospora caninum in beef cattle.

During 1999, serum samples were collected from beef cows on pastures in western Canada. Some of the herds had a history of confirmed abortions associated with Neospora caninum infection. All these samples were initially analyzed using a single application of 1 common commercial enzyme-linked immunosorbent assay (ELISA) for antibodies to N. caninum. From these initial results, 239 positive and 250 negative samples were randomly selected for further testing. This group of samples was retested using the 3 commercially available ELISA tests for N. caninum as per the manufacturer's recommendations. The agreement between 2 of the ELISAs was good (K = 0.76); agreement of these 2 tests with the third test was much lower (K = 0.46 and 0.60). Quantitative agreement between tests measured by intraclass correlation coefficients was also acceptable between the first 2 tests but was almost zero when the first 2 tests were compared with the third. This information is necessary to understand the differences in seroprevalence reported in different regions from laboratories using different methods.