Which statement best defines primary erythrocytosis?

Which statement best defines primary erythrocytosis?

• A. JAK2 mutation with increased RBC mass but absence of hypoxia and tri-lineage expansion
• B. Erythrocytosis due to chronic hypoxia
• C. Elevated EPO with increased leukocytes
• D. Lymphoid proliferation predominates

Answer: (A)

Primary erythrocytosis is a clonal myeloproliferative disorder in which red cell production runs on its own, driven by an activating JAK2 mutation. This leads to an increased red cell mass without the need for low oxygen levels, and the bone marrow typically shows expansion of all three myeloid lines (panmyelosis). Because the red cell mass is driven by the mutated clone, erythropoietin levels are usually suppressed or not elevated, reflecting this independence from hypoxic drive. That’s why a JAK2 mutation with increased RBC mass in the absence of hypoxia and with tri-lineage expansion best defines primary erythrocytosis. In contrast, erythrocytosis due to chronic hypoxia is a reactive process driven by high EPO, and other scenarios like elevated EPO with leukocytosis or lymphoid-predominant proliferation do not fit primary erythrocytosis.

Primary erythrocytosis is a clonal myeloproliferative disorder in which red cell production runs on its own, driven by an activating JAK2 mutation. This leads to an increased red cell mass without the need for low oxygen levels, and the bone marrow typically shows expansion of all three myeloid lines (panmyelosis). Because the red cell mass is driven by the mutated clone, erythropoietin levels are usually suppressed or not elevated, reflecting this independence from hypoxic drive. That’s why a JAK2 mutation with increased RBC mass in the absence of hypoxia and with tri-lineage expansion best defines primary erythrocytosis. In contrast, erythrocytosis due to chronic hypoxia is a reactive process driven by high EPO, and other scenarios like elevated EPO with leukocytosis or lymphoid-predominant proliferation do not fit primary erythrocytosis.