What is Hemagglutination assay?

Hemagglutination assay:

1. It is the most popular indirect method of counting virus particles.
2. Several viruses bind to the surface of RBCs (red blood cells). In case the ratio of viruses to that of cells is large, the virus particles can join red blood cells thus forming a network that settles out of the suspension or agglutinates.
3. RBCs are mixed with many virus preparation dilutions where each mixture is analyzed. Hemagglutination is caused by the hemagglutination titer which is the highest dilution of viruses.
4. This type of essay is a rapid and accurate method to find the comparative quantity of viruses such as the influenza virus.