Which three factors affect the position of the oxygen dissociation curve?

• A. pH, CO2, Temperature
• B. Oxygen partial pressure alone
• C. Haematocrit
• D. Platelet count

Answer: (A)

The position of the oxygen dissociation curve shows how readily hemoglobin releases oxygen and is shifted by conditions that change hemoglobin’s affinity for oxygen. A rightward shift means Hb has lower affinity, so it unloads oxygen more readily to tissues; a leftward shift means higher affinity, keeping oxygen bound more tightly. pH and CO2 drive the Bohr effect: when CO2 levels rise and pH falls (more H+), hemoglobin’s affinity for oxygen decreases, shifting the curve to the right. Temperature also influences affinity—higher body temperature reduces Hb’s oxygen affinity, causing a rightward shift. Therefore, the three factors that affect the curve’s position are pH, CO2, and temperature. Oxygen partial pressure alone describes the curve but doesn’t move it; hematocrit changes oxygen carrying capacity rather than Hb’s affinity, and platelet count has no effect on the curve.