Splenic red cell pooling: a diagnostic feature in polycythaemia.

Total red cell volumes and splenic red cell pools were measured in 31 patients with polycythaemia. 22 had polycythaemia vera (PV), 12 of whom had clinically detectable splenomegaly, and nine patients had secondary polycythaemia (PS). The mean red cell pool was 192.8 ml (SD 126.6) in PV (all cases), and 130.9 ml (SD 28.4 ml) in PV without splenomegaly; it was 61.1 ml (SD 8.3 ml) in PS. When expressed relative to spleen size (in cm), differences were even more striking: PV (all cases)--mean 13.7 ml/cm (SD 4.3); PV without splenomegaly--mean 12.7 ml/cm (SD 2.2); PS--mean 6.6 ml/cm (SD 1.2). Measurement of splenic red cell pool thus appears to be a valuable diagnostic tool for distinguishing between PV and PS. The findings point to the presence in PV of a splenic structural abnormality which is not simply an effect of the increased circulating red cell mass.