Investigating the Role of Laboratory and Antigen in Repeatability of Results in Newcastle Virus Hemagglutination Inhibition

Hemagglutination Inhibition (HI) test is a universal method in veterinary laboratories that has low sensitivity and high specificity in determining the level of antibody. This study aimed to evaluate the repeatability of HI test and to determine the suitable antigen for HI test. Two experiments were conducted in this study. In the first, 60 serum samples were divided into four groups, including negative, low, medium, and high titer serums for Newcastle virus. Also, to evaluate the repeatability of the HI test results, eight pairs of repeating serums were placed from all four serum groups. The sera were sent to 11 different veterinary laboratories, and asked to determine the Newcastle HI titers by standard protocols. In second experiment, 41 sera were used to determine the appropriate antigen using five antigens (Clone Lasota, Lasota, B1, commercial and laboratory antigen) for the HI test. the first experiment showed that most laboratories could identify high titers, but there is a significant difference in determining zero, low, and medium titers. Also, based on results obtained from each of laboratories, it was found that the reproducibility of HI results within a laboratory is low.  In the second experiment, the best antigen was determined in terms of the same answers for use in the HI antigen test of Lasota Clone vaccine. This study is the first study on the quality control of the HI in Iran. The results showed that the quality of test is not satisfactory, and the IVO and research centers should standardize this test.