COMPARISON OF INFLUENZA SEROLOGICAL TECHNIQUES BY INTERNATIONAL COLLABORATIVE STUDY

An international collaborative study was performed to investigate the reproducibility of influenza serological techniques. Participants in s even laboratories representing five countries measured antibody to A/S ichuan/2/87 (H3N2), A/Taiwan/1/86 (H1N1) and B/Beijing/1/87 influenza viruses in 11 human sera and three postinfection ferret sera. Two diff erent serological techniques were used, haemagglutination inhibition ( HI) and single-radial haemolysis (SRH) and, although each technique wa s reproducible within laboratories, variability between laboratories w as higher for HI (maximum variability 32-fold; geometric coefficient o f variation, GCV, 112%) than for SRH (maximum variability 3.8-fold; GC V 57%). The use of a standard serum allowed direct comparison of HI an d SRH data and, for each technique, a standard serum improved inter-la boratory agreement. For influenza A viruses there was a correlation be tween HI and SRH antibodies (correlation coefficient similar to 0.9). An HI titre of 1:40 in human sera corresponded to an SRH titre of 19-3 3 mm(2). The results of the study indicate that two sera would be expe cted to contain different antibody levels if their HI titres differed by >fourfold and SRH areas differed by >50%. Both SRH and HI possessed equivalent sensitivity for measurement of antibody to influenza A vir uses but SRH was more sensitive for detection of antibody to influenza B viruses. The study provided valuable information about standardizat ion of antibody assays.