Premature destruction of red cells occurs through two primary mechanisms: (1) decreased erythrocyte deformability that leads to red cell sequestration and extravascular haemolysis in the spleen and other components of the reticuloendothelial system—may be caused by membrane defects, metabolic abnormalities, exogenous oxidizing agents, or pathological antibodies; and (2) red cell membrane damage and intravascular haemolysis—may be caused by exposure to pathological antibodies, activated complement, mechanical forces, chemicals, and infectious agents. Congenital haemolytic anaemias—congenital disorders resulting in a haemolytic anaemia include (1) disorders of the red cell membrane such as hereditary spherocytosis and hereditary elliptocytosis; (2) disorders of red cell enzymes such as glucose-6-phosphate dehydrogenase deficiency and pyruvate kinase deficiency; and (3) disorders of globin structure. Acquired immune haemolytic anaemias—immune haemolysis may occur when IgG, IgM, or IgA antibodies and/or complement bind to the erythrocyte surface. Autoimmune haemolytic anaemias—these are best classified according to the temperature at which the antibody optimally binds to the erythrocyte: warm autoimmune haemolytic anaemia, cold agglutinin-mediated autoimmune haemolytic anaemia, paroxysmal cold haemoglobinuria, and mixed type autoimmune haemolytic anaemia. Drug-induced haemolytic anaemia—haemolysis can be caused by drugs that induce a positive DAT. Drug-induced antibodies may be drug dependent or drug independent depending on whether the presence of the drug is required for their detection. Alloimmune haemolytic anaemias—these include acute haemolytic transfusion reactions and other conditions such as delayed haemolytic transfusion reactions, passenger lymphocyte haemolysis, and haemolytic disease of the newborn. Acquired nonimmune haemolytic anaemias and microangiopathic haemolytic anaemia are also discussed in this chapter.
How to use Donath-Landsteiner test to diagnose paroxysmal cold haemoglobinuria (PCH)
