The Influence of Test Conditions on Newcastle Disease Hemagglutination-Inhibition Titers

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Abstract
Replicate samples of serum from chickens immune to Newcastle disease were titrated to determine the influence of certain test conditions on hemagglutination-inhibition (HI) titers. The test conditions studied were those most likely to vary in normal laboratory operations. The most marked effect on magnitude of HI titers was incubation time of 2-fold serum dilutions in antigen-saline; the average titer increase after incubation of the serum-antigen mixture for 1 h at 37.degree. C was log2 2.3 (5-fold). Twofold increases in virus concentration of the antigen-saline diluent caused an average titer reduction of log2 0.8. Shifts in HI titers were only minor with 2-fold changes in erythrocyte concentration (log2 0.3), with variations of test reading times from 0.5-2.0 h (log2 0.1), and with variations in the period between preparation of the initial 1:10 serum dilution in antigen-saline and the subsequent serum dilutions (log2 0.3).