The hemagglutination-inhibition (HAI) test is a common test for the serological diagnosis of virus infections. Viruses have surface proteins that attach to red blood cells and cause them to agglutinate (hemagglutination). The basis for the hemagglutination-inhibition test (HAI) is antibodies against the viral protein will prevent the virus induced hemagglutination. Serum from the animal is tested to determine the minimum dilution that inhibits the hemagglutination. This is reported as the HAI titer of the serum.
A number of HAIs are offered targeting influenza strains H1N1, H3N2, H5N1, H7N9 and H10N8.