erythrocytosis

Erythrocytosis is an abnormal increase in red blood cell mass. It can be absolute, reflecting a true expansion of red cells, or relative, caused by a fall in plasma volume. Absolute erythrocytosis is further categorized as primary, due to a clonal bone marrow disorder, or secondary, due to elevated or inappropriately regulated erythropoietin (EPO) activity.

Primary absolute erythrocytosis includes polycythemia vera and related myeloproliferative neoplasms, usually associated with a JAK2 mutation (most cases). Secondary absolute erythrocytosis arises from increased EPO production or response, commonly in settings of chronic hypoxia (high altitude, chronic lung disease, obstructive sleep apnea, smoking) or from EPO-producing tumors such as kidney or liver cancers.

Relative erythrocytosis results from a reduction in plasma volume, for example from dehydration or diuretic use, giving a normal red cell mass but a higher concentration of cells.

Diagnosis starts with a complete blood count showing elevated hemoglobin and hematocrit. Further workup includes measurement of red cell mass, serum EPO level, and testing for JAK2 mutations when polycythemia vera is suspected; bone marrow examination is not routinely required unless the PV diagnosis remains uncertain. Additional evaluations may identify secondary causes such as hypoxemia or tumors.

Treatment depends on the underlying cause. In polycythemia vera, management aims to reduce thrombotic risk with therapeutic phlebotomy to maintain a target hematocrit, low-dose aspirin, and risk-adapted cytoreductive therapy for high-risk patients; iron status should be preserved. In secondary erythrocytosis, management focuses on treating the underlying condition (supplemental oxygen for hypoxemia, smoking cessation, treating tumors) and correcting volume status as appropriate.

Erythrocytosis increases thrombosis risk, especially in polycythemia vera. Prognosis and management depend on the cause and comorbidity, with regular monitoring of hematologic parameters and cardiovascular risk factors.