Standardization of Hemagglutination Inhibition Assay for Influenza Serology Allows for High Reproducibility between Laboratories

Abstract

Standardization of the hemagglutination inhibition (HAI) assay for influenza serology is challenging. Poor reproducibility of HAI results from one laboratory to another is widely cited, limiting comparisons between candidate vaccines in different clinical trials and posing challenges for licensing authorities. In this study, we standardized HAI assay materials, methods, and interpretive criteria across five geographically dispersed laboratories of a multidisciplinary influenza research network and then evaluated intralaboratory and interlaboratory variations in HAI titers by repeatedly testing standardized panels of human serum samples. Duplicate precision and reproducibility from comparisons between assays within laboratories were 99.8% (99.2% to 100%) and 98.0% (93.3% to 100%), respectively. The results for 98.9% (95% to 100%) of the samples were within 2-fold of all-laboratory consensus titers, and the results for 94.3% (85% to 100%) of the samples were within 2-fold of our reference laboratory data. Low-titer samples showed the greatest variability in comparisons between assays and between sites. Classification of seroprotection (titer > 40) was accurate in 93.6% or 89.5% of cases in comparison to the consensus or reference laboratory classification, respectively. This study showed that with carefully chosen standardization processes, high reproducibility of HAI results between laboratories is indeed achievable.T he hemagglutination inhibition (HAI) assay is the primary method for determining quantitative antibody titers for influenza virus and is widely used both for licensure of vaccines and for seroepidemiologic studies examining protection in populations (1-3). The assay relies on the ability of the hemagglutinin protein on the surface of influenza virus to bind to sialic acids on the surface of red blood cells (RBCs) (4). If the patient's serum contains antibodies that block viral attachment, this interaction is inhibited. Direct comparison of results between studies has been problematic, as the reproducibility of HAI assays between laboratories has historically been poor (5-12). These studies have shown that HAI titers reported for identical specimens in different laboratories can vary as much as 80-fold or 128-fold (9, 11), with the geometric coefficient of variation (GCV) as high as 803% (5). This variability in results may relate to differences in biological reagents, protocols, and personnel training. The use of international standards (IS) may reduce interlaboratory variability (6, 11, 13), but such reagents currently exist only for influenza A H1N1 and H5N1 clade 1 viruses (14, 15). The need for standardization of HAI assays and other laboratory methods (e.g., microneutralization [MN] assays) has been highlighted as a priority of CONSISE, the Consortium for the Standardization of Influenza Seroepidemiology (16,17). CONSISE collaborators have recently published data showing that a standardized MN protocol improves the comparability of serologic results between laboratories (18); however, the conso...

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