The differential diagnosis of the polycythemic states.

The clinical and laboratory characteristics that are essential for the differential diagnosis of the polycythemic states are reviewed. The various forms of polycythemia that present as increases in hemoglobin concentration or packed red cell volumes can often be distinguished on the basis of pathophysiology, predisposition to neoplasia, hematological and viral parameters, chromosomal patterns, and response to therapy. Polycythemia vera differs from secondary and relative polycythemic states in its basic pathophysiology and etiology. It appears to be a clonal disorder that is characterized by a generalized bone marrow panmyelosis. Although the primary event leading to this stem cell disorder is not known, recent studies suggest a possible etiology. Therapeutic regimens based on the parameters inherent in making a differential diagnosis of the polycythemic states are discussed. Prognosis for polycythemia vera also appears to be predicated by the choice of drugs used to treat the disease. The consequences of making the correct diagnosis and of choosing appropriate therapy in light of the differences in underlying pathophysiology and etiology of the polycythemic states are stressed.