Which statement about Hb F is true?

Which statement about Hb F is true?

• A. Hb F has lower affinity for oxygen than Hb A
• B. Hb F is the majority Hb in adults
• C. Hb F has higher affinity for oxygen than Hb A
• D. Hb F is absent after birth

Answer: (C)

Fetal hemoglobin binds oxygen more tightly than adult hemoglobin because it contains gamma chains instead of beta chains, which reduces binding by 2,3-BPG. This shifts the oxygen dissociation curve to the left, so Hb F holds onto oxygen more readily at the same partial pressure. In the placenta, where maternal blood has higher oxygen tension, Hb F can efficiently take up oxygen for transfer to the fetus. After birth, Hb F levels fall as Hb A becomes predominant, and small amounts of Hb F can remain in adults, so it isn’t absent. This higher affinity of Hb F for oxygen makes the statement true.

Fetal hemoglobin binds oxygen more tightly than adult hemoglobin because it contains gamma chains instead of beta chains, which reduces binding by 2,3-BPG. This shifts the oxygen dissociation curve to the left, so Hb F holds onto oxygen more readily at the same partial pressure. In the placenta, where maternal blood has higher oxygen tension, Hb F can efficiently take up oxygen for transfer to the fetus. After birth, Hb F levels fall as Hb A becomes predominant, and small amounts of Hb F can remain in adults, so it isn’t absent. This higher affinity of Hb F for oxygen makes the statement true.