Altitude, smoking, lung disease, cyanotic heart disease can all cause ___________ polycythemia

• A. Primary
• B. Secondary
• C. Polycythemia Vera
• D. Relative

Answer: (B)

The key idea is how the body increases red blood cell mass in response to low oxygen. Secondary polycythemia arises when hypoxia from any cause stimulates the kidneys to make more erythropoietin, driving extra red cell production. Altitude lowers ambient oxygen, smoking and its carbon monoxide lower oxygen delivery, lung disease impairs gas exchange, and cyanotic heart disease causes poorly oxygenated blood; all trigger increased erythropoietin and a true rise in red cells.

In contrast, primary polycythemia (polycythemia vera) is a bone marrow disorder driven by a JAK2 mutation, with high red cell mass not due to hypoxia and often suppressed erythropoietin. Relative polycythemia is due to plasma volume loss, giving a high hematocrit without an actual rise in red cell mass.