Differential polycythemia: a comparative study between spurious polycythemia and pure erythrocytosis.

The definite differential diagnosis between spurious polycythemia (SP) and pure erythrocytosis (PE) was tested. Serum erythropoietin (EPO) levels in 6 patients with PE were 12.8 +/- 3.7 mU/ml and were significantly lower than those of both 19 normal controls (28.5 +/- 15.0 mU/ml) and 9 patients with SP (21.3 +/- 10.2 mU/ml). Three of 11 patients with SP and 1 of 3 patients with PE had significantly higher marrow erythroid progenitor cells (CFU-Es) than those of the normal controls. Spontaneous CFU-E growth (CFU-E growth in the absence of added EPO) was found in 4 of 11 patients with SP, 1 of 3 patients with PE, and all patients with polycythemia vera. However, the number of spontaneous CFU-E was low in SP and PE. The measurements of serum EPO levels and CFU-E growth did not provide differentiation between PE and SP. Even if some patients, whose total red cell volumes are either higher than 12.5% above the mean predicted values or their CFU-E growth is great, are diagnosed as SP, consideration should be made that they might, in fact, have PE.