A 60-year-old man receives 8 units of packed red blood cells over 2 hours for massive upper GI bleeding. He develops perioral tingling, carpopedal spasm, and the ECG shows prolonged QT interval. Serum calcium is 6.8 mg/dL (corrected). What is the most likely mechanism?

• A Citrate in stored blood binds ionized calcium ✓
• B Massive transfusion causes hyperparathyroid crisis
• C PRBCs contain high levels of phosphate causing calcium precipitation
• D Hypothermia from stored blood impairs calcium absorption

Explanation

Citrate, the anticoagulant in stored blood products, chelates ionized calcium when infused rapidly or in large quantities, particularly in patients with impaired hepatic metabolism. This causes symptomatic hypocalcemia manifesting as neuromuscular irritability, prolonged QT interval, and cardiac dysfunction. Treatment is intravenous calcium chloride or gluconate. Each unit of PRBCs contains approximately 3 g of citrate, which is normally metabolized by the liver within minutes.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.