2,3-DPG effects on PO2

BeMo Free Repeat™ On Us + MCAT 520 Challenge™
This forum made possible through the generous support of SDN members, donors, and sponsors. Thank you.


In an EK101 Physiology passage, it presents a patient who experiences delayed breathing, headache, and dizziness after arriving in a high-altitude city. The question asks "which of the following curves most likely represents the oxyhemoglobin dissociation curve of the patient in this passage?"

The answer shows a left shift in the oxygen dissociation curve and the explanation is, "The left shift in the curve would allow the hemoglobin molecule to drop off more oxygen in the tissues."

Wouldn't it be the opposite? If there is a left shift, wouldn't that represent an increased affinity for O2 by Hb, meaning less O2 gets dropped off at the tissues? I thought this would be the opposite of what we want our body to do in high altitudes :/


Full Member
5+ Year Member
Nov 1, 2015
Reaction score
I believe it should be a shift to the right. You specifically want your hemoglobin to have less affinity for O2 at the tissue level so that you can drop off more O2 at the tissues. At high altitudes, we know that more 2,3-BPG is made, which shifts the curve to the right.
  • Like
Reactions: 1 user


Full Member
2+ Year Member
Jun 6, 2017
Reaction score
Maybe we can see a picture of the problem? There may be a discrepancy between the way it's posted. I say that because the question states "after arriving," the patient is experiencing symptoms of hypoxia. This is trying to say that the patient has not yet adapted to the high-altitude. Yes, 2,3-BPG causes a right shift in the oxyhemoglobin curve like you're saying, but it's not immediate; it's an adaptation. So I'm inclined to think that the patient does have an oxyhb curve that is more to the left than it should be of an acclimated resident. A left shift per se? No, it shouldn't shift. But more left than normal? Yes.