MCQ – 93771

In a packed RBC transfusion, which of the following oxygen dissociation curves is observed?

A.	Curve B
B.	Curve C
C.	Curve D
D.	Curve E

Show Answer

Correct Answer » A Explanation

• Curve A represents the normal oxygen–hemoglobin dissociation curve.
• Curve B shows a left shift (increased oxygen affinity).
• Curve D shows a right shift (decreased oxygen affinity).
• Curve C represents myoglobin (very high affinity, hyperbolic curve).
• Curve E represents dissolved oxygen (linear relationship).

Explanation of the Clinical Concept

• Stored packed RBCs have decreased 2,3-Bisphosphoglycerate (2,3-BPG).
• 2,3-BPG normally decreases hemoglobin’s affinity for oxygen, facilitating oxygen release.
• When 2,3-BPG decreases → hemoglobin holds oxygen more tightly.

Explanation of the Correct Answer (Curve B – Left Shift)

• Decreased 2,3-BPG → leftward shift of the dissociation curve
• Left shift means:
  • Increased oxygen affinity
  • Reduced oxygen delivery to tissues
• Therefore, packed RBC transfusion corresponds to Curve B

Explanation of Other Options

B. Curve C

• Represents myoglobin
• Not related to hemoglobin changes in transfusion

C. Curve D

• Represents right shift
• Seen in acidosis, increased CO₂, increased temperature
• Opposite of stored blood effect

D. Curve E

• Represents dissolved oxygen in plasma
• Not relevant to hemoglobin behavior