Which biochemical change does not occur in stored blood?

• A. Plasma K+ decreases
• B. Plasma pH decreases
• C. Plasma Na+ decreases
• D. 2,3-DPG decreases

Answer: (A)

Stored blood undergoes several predictable biochemical changes over time. Potassium, which is predominantly inside red cells, leaks out into the plasma as the cell membranes become more permeable during storage. This causes plasma potassium to rise, not fall. At the same time, ongoing glycolysis produces lactic acid, so the plasma pH drops. 2,3-DPG, which helps hemoglobin release oxygen, gradually decreases during storage, shifting the oxygen affinity of hemoglobin. Sodium, on the other hand, does not show a consistent downward trend during storage and remains relatively stable compared with these other changes.

Thus, a decrease in plasma potassium is not a change that occurs in stored blood; potassium actually increases, making that option the one that does not occur.