Increasing HbA relative to HbF in neonates is associated with which shift in the ODC?

• A. Left Shift
• B. Right Shift
• C. No Shift
• D. Unrelated

Answer: (B)

Oxygen dissociation curve shifts reflect changes in hemoglobin’s oxygen affinity. A rightward shift means lower affinity (higher P50) so hemoglobin releases oxygen more readily to tissues; a leftward shift means higher affinity (lower P50) making loading in the lungs easier.

Fetal hemoglobin has a higher oxygen affinity than adult hemoglobin because of its structure and reduced 2,3-BPG binding. This makes the ODC left-shifted when HbF is dominant. If HbA increases relative to HbF in neonates, the overall hemoglobin population has a lower oxygen affinity, so the curve shifts to the right. This right shift indicates that oxygen is unloaded more readily to tissues, which is expected as the newborn transitions from fetal to postnatal circulation.