Linked from
The 13 pages that link to Agglutination, each with the reason it gives.
SerologyRelated: Visible clumping provides a direct readout in several serological tests.
Blood typingRelated: Visible agglutination is a common signal in serological blood-group tests.
Karl LandsteinerRelated: Visible clumping let Landsteiner distinguish incompatible blood samples.
Blood typeRelated: Antibody binding can visibly clump incompatible red cells during testing.