Polycythemia is an increase above the normal range of RBCs in the circulation. Concern that the Hb level may be abnormally high should be triggered at a level of 170 g/L (17 g/dL) in men and 150 g/L (15 g/dL) in women. Polycythemia is usually found incidentally at routine blood count. Relative erythrocytosis, due to plasma volume loss (e.g., severe dehydration, burns), does not represent a true increase in total RBC mass. Absolute erythrocytosis is a true increase in total RBC mass.
Polycythemia vera (a clonal myeloproliferative disorder), erythropoietin-producing neoplasms (e.g., renal cancer, cerebellar hemangioma), chronic hypoxemia (e.g., high altitude, pulmonary disease), carboxyhemoglobin excess (e.g., smokers), high-affinity Hb variants, Cushing's syndrome, androgen excess. Polycythemia vera is distinguished from secondary polycythemia by the presence of splenomegaly, leukocytosis, thrombocytosis, and elevated vitamin B12 levels, and by decreased erythropoietin levels and the presence of a mutation in the JAK2 kinase (V617F). An approach to evaluate polycythemic pts is shown in Fig. 47-2. An Approach to the Differential Diagnosis of Pts with an Elevated Hemoglobin (Possible Polycythemia).
Hyperviscosity (with diminished O2 delivery) with risk of ischemic organ injury and thrombosis (venous or arterial) are most common.
| TREATMENT | ||
PolycythemiaPhlebotomy recommended for Hct≥55% to low-normal range. Aspirin is routinely given to lower the thrombosis risk. For those in whom phlebotomy is inadequate, hydroxyrurea may be used to control the hematocrit level. |