<s>[INST] context: Make it very clear in mind that the higher affinity of fetal hemoglobin for oxygen is due to the low affinity of HbF for 2,3 - DPG (not due to decreased 2, 3-DPG concentration). HbF does not combine to 2, 3-DPG as avidly as adult hemoglobin.
"Fetal hemoglobin is left - shifted because it has a low affinity for DPG". — Principles of medical physiology
"It is worth noting that DPG does not combine with fetal hemoglobin. That is perhaps one reason why HbF has a greater affinity for oxygen than adult hemoglobin (HbF)". — Understanding of medical physiology
"Fetal hemoglobin binds less 2-3 DPG it has consequently a greater affinity for O2". _ Pediatric physiology
All other textbooks have mentioned the same thing.
So, the high affinity of HbF to O2 is due to the low affinity of HbF for 2, 3 DPG (and not due to decreased 2, 3-DPG concentration).
However, amongst the given options, option a is the best answer here because, although there is no decrease in concentration of 2, 3-DPG, because of low affinity for 2, 3-DPG, HbF behaves as if 2, 3-DPG levels are low.
"Fetal hemoglobin has considerably less affinity for 2, 3-DPG than does adult hemoglobin. In human blood, the affinity of fetal hemoglobin for 2, 3-DPG is only about 40% that of adult hemoglobin. This makes fetal hemoglobin behave as if 2, 3-DPG levels are low; therefore, the oxygen dissociation curve is shifted to the left". — Clinical physiology in childhood [/INST] question: Fetal hemoglobin has a higher affinity for oxygen due to | options: A: Low affinity for 2, 3 DPG B: Reduced pH C: Increased release of carbon dioxide D: Oxygen dissociation curve is shifted to right | answer: A </s>