POLYCYTHAEMIA

Abstract

This chapter describes the causes and diagnosis of polycythemia. Polycythemia denotes a significant increase in the body's total red cell mass above the normal value of 25–35 ml per kg of body weight. The diagnosis is suspected from the clinical appearance of the patient or from a routine-blood count that shows considerable increase in circulating hemoglobin content, red-cell count, and packed-cell volume. The increase in the hemoglobin content is usually rather less in proportion to the increase in the red cells, and it is not unusual to find the red cells reduced in cell volume. The total blood-volume is usually normal or increased and as a result of the increase in red cell mass, there is an increase in blood viscosity. This may double in value with a rise in packed-cell volume from 45 to 55%. A relative polycythemia results from a reduction in the plasma volume, the red-cell mass remaining constant, and may occur when, for any reason, there is a considerable loss of fluid from the circulation.