What is the significance of polycythemia in COPD?

• A. It reduces blood viscosity and improves flow
• B. It has no clinical significance
• C. It results from chronic hypoxia and increases blood viscosity, leading to complications
• D. It decreases RBC mass

Answer: (C)

In COPD, chronic low blood oxygen levels trigger the kidneys to make more erythropoietin, increasing red blood cell production and causing polycythemia. This raises the hematocrit and makes the blood thicker (higher viscosity). When blood is more viscous, flow through the microcirculation slows, oxygen delivery to tissues can actually worsen despite more red cells, and the risk of clotting rises. That means polycythemia has real clinical consequences, including higher chances of thrombosis, potential strain on the heart, and progression toward right‑sided heart problems. So the significance is that polycythemia is a compensatory response to hypoxia that can lead to hyperviscosity and its complications. The other statements conflict with the physiology (viscosity does not decrease; it’s not clinically insignificant; RBC mass does not decrease).