During citrate anticoagulation, ionized calcium levels are typically:

• A. Increase
• B. Decrease
• C. Unchanged
• D. Fluctuate

Answer: (B)

Citrate anticoagulation works by binding free calcium in the blood, forming calcium-citrate complexes and removing ionized calcium. Ionized calcium is the active form needed for the coagulation cascade and platelet function, so its reduction in the circuit effectively prevents clot formation. To keep the patient safe, calcium is often replenished systemically to maintain normal systemic calcium levels, while the circuit remains depleted of ionized calcium. Because of this setup, ionized calcium levels in the circuit are typically decreased rather than increased, unchanged, or fluctuating unpredictably.