Polycythemia: a manifestation of heart disease, lung disease or a primary blood dyscrasia.

ary polyeythemia is diagnosed when the patient has polycythemia associated with cyanotic heart disease or lung disease in the absence of leukoeytosis, high platelet count, and splenic enlargement. The differentiation of polycythemia vera from secondary polycythemia is sometimes a difficult task. Ratto, Briscoe, Morton, and Comroel have discussed the theoretical reasons that make this distinction possible by measuring arterial oxygen saturation. Also they point out the practical obstacles. The hypothesis is that uncomplicated polycythemia vera should not lead to arterial hypoxemia. No disturbance in pulmonary ventilation, pulmonary circulation, or in the ability of oxygen to diffuse from the alveolus into the red blood cell has been demonstrated in patients with polyeythemia vera. If the oxygen saturation of arterial blood is reduced in patients with polyeythemia, this suggests that polycythemia is secondary to hypoxemia. This conelusion is questionable because arterial