What happens to blood cells during hemagglutination?

During hemagglutination, blood cells, specifically red blood cells, clump together due to the interaction between viral hemagglutinin and specific receptors on the surface of the red blood cells. This process is often utilized in microbiological tests to determine the presence of viruses or antibodies.

When a virus with hemagglutinin is present, it binds to sialic acid residues on the red blood cell membranes, leading to the aggregation of multiple red blood cells. This clumping can visually manifest as a sedimentation pattern in laboratory tests, which is a crucial indicator for various hematological assays and viral presence.

The other options do not accurately describe the phenomenon of hemagglutination. In this context, blood cells do not separate, swell, or change their shape in a manner that characterizes hemagglutination. Instead, the defining aspect of this process is the formation of aggregates or clusters of red blood cells.