A leftward shift in the oxyhemoglobin dissociation curve is caused by decreased 2,3-DPG in stored red blood cells. What is the net effect on oxygen unloading?

A leftward shift in the oxyhemoglobin dissociation curve is caused by decreased 2,3-DPG in stored red blood cells. What is the net effect on oxygen unloading?

• A. Increased oxygen unloading to tissues
• B. Increased oxygen affinity, making unloading harder
• C. Decreased oxygen affinity, easier unloading
• D. No change in affinity

Answer: (B)

The key idea is how 2,3-DPG shapes the oxyhemoglobin dissociation curve. When 2,3-DPG levels fall, as in stored red blood cells, hemoglobin’s affinity for oxygen increases, shifting the curve to the left. A leftward shift means hemoglobin binds O2 more tightly and releases it less readily at tissues. This is captured by a lower P50 (the PO2 at which Hb is 50% saturated). So, even though loading O2 in the lungs remains favorable, unloading at tissues becomes harder. The net effect is increased oxygen affinity, making unloading harder. Stored blood may thus deliver less O2 to tissues until 2,3-DPG levels rebound in circulation.

The key idea is how 2,3-DPG shapes the oxyhemoglobin dissociation curve. When 2,3-DPG levels fall, as in stored red blood cells, hemoglobin’s affinity for oxygen increases, shifting the curve to the left. A leftward shift means hemoglobin binds O2 more tightly and releases it less readily at tissues. This is captured by a lower P50 (the PO2 at which Hb is 50% saturated). So, even though loading O2 in the lungs remains favorable, unloading at tissues becomes harder. The net effect is increased oxygen affinity, making unloading harder. Stored blood may thus deliver less O2 to tissues until 2,3-DPG levels rebound in circulation.