A comparison of infectious bronchitis virus hemagglutination-inhibition test procedures

Replicate hemagglutination-inhibition (HI) tests of selected convalescent and hyperimmune infectious bronchitis virus (IBV) antisera were run against five IBV antigens: Massachusetts 41, Connecticut 46, H52, Arkansas 99, and JMK. Six different HI test procedures were included in this comparison to evaluate the effect of procedural differences on HI titers. The results were similar among procedures to the extent that positive and negative reactions were differentiated by each procedure with each antigen. This indicated that specificity was not affected by the procedure. However, the mean titers did differ among procedures in tests of the same serum-antigen combination, and the range of the titer differences was frequently fourfold or greater. Generally, high or low titers were associated with specific procedures, regardless of which test antigen was used.