When citrate is present in the circuit, which ion should be monitored?

• A. Sodium
• B. Potassium
• C. Ionized Calcium
• D. Magnesium

Answer: (C)

Citrate works by binding calcium, which is essential for coagulation. Because of this, the ionized (free) calcium level is the key measure to monitor. Tracking ionized calcium tells you how strong the anticoagulation in the circuit is and whether the patient’s systemic calcium is dropping too low when citrate is returned to circulation. If ionized calcium falls toward the lower end, calcium infusion is adjusted to prevent hypocalcemia while maintaining circuit anticoagulation. Ionized calcium is favored over total calcium because it reflects the active calcium available for physiological processes, whereas total calcium includes calcium bound to proteins or citrate and doesn’t indicate active Ca2+ levels.