hemagglutination inhibition test (HAI)

Indications

• determination of antibodies directed against influenza virus
• assessment of immunity to influenza

Principle

• influenza virus particles contain an envelope protein called hemagglutinin which binds to sialic acid receptors on cells, including erythrocytes
• viruses thus agglutinate RBCs via hemagglutinin binding to RBCs
• antibodies directed against these viruses will inhibit hemagglutination
• hemagglutination inhibition is thus a measure of antibodies direct against hemagglutinating viruses

Clinical significance

• a titer of 1:40 is associated with a 50% reduction in risk of influenza

More general terms

• clinical hematology test

Additional terms

• influenza
• Orthomyxoviridae (influenza virus)