Difference Between Agglutination and Coagulation

Agglutination and coagulation are two very technical terms which rarely come up unless you are a medical professional. These two terms refer to two different phenomena; however, agglutination makes only a tiny part in the coagulation cascade.


Agglutination is the process of clumping of particles. There are many examples of agglutination. Hemagglutination is the coming together of red blood cells. Leukoagglutination is the clumping of white blood cells. Bacterial antigens agglutinate with antibodies making diagnosis easier. Blood grouping is another common example where agglutination is used to make a diagnosis. There are complex mechanisms behind these particles coming together and forming a clump.

Cells have receptors on their surfaces. These receptors bind with selective molecules outside the cells. Blood grouping is a good example that can be used to explain this simply. There are four major blood types. They are A, B, AB and O. A, B and AB refer to the presence of specific antigens (A antigen, B antigen) on red cell surfaces. O means that there is neither A or B antigen on red cell surfaces. If A antigen is there on the red cell surfaces, anti-A antibody is not there in plasma. B blood group has anti-A antibodies in plasma. AB blood group does not have either. O blood group has both A and B antibodies. A antigen binds with A-antibody. When B blood is mixed with A blood, due to the presence of anti-A antibodies in plasma, red cells bind with these antibodies. More than one red cell bind with one antibody, so there is a crosslinking; this is the basis of red cells coming together. This is the basis of clumping.


Coagulation is the process of blood clotting. Clotting has three major steps. They are platelet plug formation, intrinsic or extrinsic pathways, and the common pathway. Trauma to platelets and endothelial cells lining the blood vessels releases chemicals, which activate and aggregate platelets. Trauma to cells releases histamine first. Then other inflammatory mediator like serotonin, major basic proteins, prostaglandin, prostacyclin, leukotrienes, and platelet acting factor come into play. Due to these chemicals, there is an agglutination of platelets. The end result is the formation of the platelet plug.

Exposure of reactive extracellular matrix material triggers two chain reactions, namely the extrinsic and intrinsic pathways. These two pathways end by activating factor X. Factor X activation is the initial step of the common pathway. The common pathway leads to the formation of a fibrin mesh, on which blood cells get trapped, and a definitive clot is formed.

Certain diseases affect coagulation. Hemophilia is a condition where a lack of coagulation factors leads to poor clotting and excessive bleeding. Abnormal clotting and inappropriate clotting lead to devastating conditions like strokes and myocardial infarction. 

What is the difference between Agglutination and Coagulation?

• Agglutination means the coming together of particles while coagulation means the formation of a definitive blood clot.

• Many particles can agglutinate while only blood can coagulate.

• Agglutination is due to an antigen-antibody reaction while coagulation is due to activation of multiple plasma factors.