All of the following characterize stored packed red blood cells kept for 35 days at 4° C in CPDA-1 except:

All of the following characterize stored packed red blood cells kept for 35 days at 4° C in CPDA-1 except:

• A. Serum potassium greater than 70 mEq/L
• B. pH less than 7.0
• C. Blood glucose less than 100 mg/dL
• D. P50 of 28

Answer: (D)

Stored packed red blood cells develop a storage lesion over time. Even with CPDA-1 at 4°C, several changes occur: potassium leaks out of the cells into the plasma, so extracellular potassium rises (often quite high, well over normal levels); glycolysis continues slowly and acid byproducts accumulate, lowering the pH below normal (often under 7.0); glucose is consumed by the cells, so stored units have lower glucose levels. A key biochemical change is loss of 2,3-DPG during storage, which shifts the hemoglobin-oxygen dissociation curve to the left, increasing oxygen affinity and reducing the P50. Because of this, the P50 in stored units tends to be lower than normal, not 28 mmHg. Therefore a P50 of 28 is not characteristic of a unit stored for 35 days; that value would be more consistent with a fresh unit.

Stored packed red blood cells develop a storage lesion over time. Even with CPDA-1 at 4°C, several changes occur: potassium leaks out of the cells into the plasma, so extracellular potassium rises (often quite high, well over normal levels); glycolysis continues slowly and acid byproducts accumulate, lowering the pH below normal (often under 7.0); glucose is consumed by the cells, so stored units have lower glucose levels. A key biochemical change is loss of 2,3-DPG during storage, which shifts the hemoglobin-oxygen dissociation curve to the left, increasing oxygen affinity and reducing the P50. Because of this, the P50 in stored units tends to be lower than normal, not 28 mmHg. Therefore a P50 of 28 is not characteristic of a unit stored for 35 days; that value would be more consistent with a fresh unit.