An improved method for the diagnosis of polycythaemia.

The red cell mass was measured in 44 normal subjects and showed a closer correlation with total body water or surface area than with body weight. The results obtained in a group of patients with polycythaemia, however, still overlap with the normal range. When the total number of circulating red cells is measured these patients form a group quite separate from the normals. The diagnostic value of this measurement is therefore considerably greater than results obtained with the red cell mass.