An agglutinin is a substance that causes particles to coagulate to form a thick mass. Agglutinins can be antibodies or any other substance like proteins that cause antigens to aggregate by binding to the antigen-binding sites of antibodies. When an agglutinin is added to a suspension of particles such as bacteria or blood, agglutinin binds to the agglutinin-specific structure on the particle causing the particles to aggregate and fall to the bottom leaving a clear suspension. This phenomenon is called asagglutination.
Cold agglutinins with low thermal capacity are usually associated with direct red blood cell agglutination at low body temperatures in the peripheral blood vessels. Cold limbs or other peripheral clotting is initiated or intensified by exposure to cold. This is a rare autoimmune disorder in which antibodies that attack red blood cells have enhanced activity at temperatures of less than 99° F (37.2° C).
Fixation of complement and hemolysis is a warm-reactive process occurring at high body temperatures; therefore, patients may have very high concentrations of cold agglutinins, but these antibodies may be unable to hemolyze red blood cells at the temperature of normal blood.
Most cold agglutinins do not cause disturbance in life span of a red blood cell. High thermal amplitude cold agglutinins may cause sustained hemolysis, but the resulting anemia is often mild and stable. Exposure to cold may enhance binding of cold agglutinins and complement mediated release of hemoglobin within the vessels called intravascular hemolysis.
A low concentration of naturally-occurring cold agglutinins may be found in healthy dogs, but this not significant. The condition is more likely to occur in colder climates.
Common symptoms would include acrocyanosis, clumps of RBCs in peripheral blood vessel, erythema, skin ulceration with crusting and necrosis, dry, gangrenous necrosis of ear tips, tail tip, nose, and feet. Affected areas may be painful. Anemia may or may not be evident: associated with pallor, weakness, tachycardia, tachypnea, jaundice, change of skin color, splenomegaly, and soft heart murmur
