Autoagglutination represents clumping of an individual's red blood cell

Red blood cell

Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...

s (RBCs or erythrocytes) by his or her own serum

Blood serum

In blood, the serum is the component that is neither a blood cell nor a clotting factor; it is the blood plasma with the fibrinogens removed...

 due to the RBCs being coated on their surface by antibodies

Antibody

An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...

.

Autoagglutination is seen to occur in a type of immune mediated hemolytic anemia known as “cold antibody hemolytic anemia

Cold antibody hemolytic anemia

Cold antibody hemolytic anemia can refer to:* Cold agglutinin disease* Paroxysmal cold hemoglobinuria...

”. Here, the antibodies which act on the erythrocytes are active at temperatures below 30 degree C.

The cold reacting antibody has maximal activity at 4 degree C and at this temperature hemolysis

Hemolysis

Hemolysis —from the Greek meaning "blood" and meaning a "loosing", "setting free" or "releasing"—is the rupturing of erythrocytes and the release of their contents into surrounding fluid...

 ,rupture of erythrocytes, is not activated.