In anemia, how is hemoglobin's oxygen dissociation characterized?

• A. 100% Hb saturation but less Hb available
• B. Hb saturation decreased due to less Hb mass
• C. Increased Hb concentration
• D. No change in oxygen delivery

Answer: (A)

In anemia, oxygen delivery hinges on oxygen content, not just how much of the Hb is saturated. The remaining hemoglobin can still be fully saturated at normal arterial oxygen tension, so Hb saturation stays high, but there is less Hb available to carry oxygen. That means total oxygen content (CaO2) falls because it scales with Hb amount, even if SaO2 is near 100%. So the best description is that you have full Hb saturation but less Hb to carry oxygen.

Why the other ideas don’t fit: saturation isn’t reduced simply because Hb mass is lowered—the affinity for oxygen at physiologic PO2 remains the same, so SaO2 can stay near 100%. Decreased Hb mass does not imply increased Hb concentration. And oxygen delivery is typically reduced in anemia due to lower CaO2, though tissues may compensate with increased blood flow; it’s not correct to say there’s no change in delivery.