The primary concern with polycythemia relates to hyperviscosity and its associated complications. This associated hyperviscosity is thought to contribute to the symptom complex observed in approximately one half of infants with polycythemia. As the central hematocrit increases, viscosity increases, resulting in abnormal blood flow kinetics. This manifests as poor flow or sludging of blood, which predisposes the infant to the development of microthrombi and decreased tissue oxygenation.
Blood viscosity is determined by multiple factors.
As previously mentioned, viscosity increases as hematocrit rises. Plasma volume, plasma proteins, platelets, and endothelial factors also contribute to viscosity. The central nervous, cardiopulmonary, gastrointestinal, and renal systems are at risk. Metabolic derangements are common. Coagulation also can be affected.