An Approach to the Patient With Erythrocytosis

Abstract

The main objective during the evaluation of an increased hematocrit or hemoglobin value is to ascertain the presence or absence of polycythemia vera (PV). However, PV is not the only cause of an increased red cell mass (RCM), and a seemingly increased hematocrit value does not always indicate a true increase in RCM.“Relative polycythemia” refers to a state of reduced plasma volume which secondarily increases the hematocrit level without an associated increase in RCM (Fig. 1). True erythrocytosis is due to either an autonomous (growth factor-independent) proliferation of erythroid cells (as in PV) or an erythropoietin (EPO)-driven secondary process, as in secondary erythrocytosis. EPO production in secondary erythrocytosis may be oxygen-sensitive (as in hypoxic conditions) or oxygen-insensitive (as in EPO-producing tumors). Oxygen-sensitive EPO production may be physiologically appropriate, as in patients with chronic lung disease, or inappropriate, as in patients with renal artery stenosis. Finally, the hematocrit level in PV may remain in the normal range because of an associated increase in plasma volume (inapparent polycythemia) (Fig. 1).