The oxygen-hemoglobin dissociation curve shifts to the right (reduced O2 affinity) in all of the following conditions EXCEPT:

• A Increased temperature (fever)
• B Increased 2,3-diphosphoglycerate (DPG)
• C Carboxyhemoglobin (CO poisoning) ✓
• D Decreased pH (acidosis) — Bohr effect

Explanation

Carboxyhemoglobin (HbCO) shifts the O2-hemoglobin dissociation curve to the LEFT (increased O2 affinity), not right — this is why CO poisoning is so dangerous: CO not only occupies binding sites (reducing O2 carrying capacity) but the remaining hemoglobin holds onto O2 more tightly and cannot release it to tissues. Temperature, 2,3-DPG, and acidosis (Bohr effect) all shift the curve rightward (reduced affinity, facilitating O2 unloading to tissues). Fetal HbF and alkalosis shift the curve leftward.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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