Ionized calcium
Background
- Physiologically active form of calcium (not bound to albumin)
- More accurate than total calcium, especially in critically ill or hypoalbuminemic patients
Normal Values
- Normal: 1.10-1.30 mmol/L (4.4-5.2 mg/dL)
Interpretation
- Preferred test in the ED for patients with low albumin, acid-base disturbances, or critical illness
- Acidosis increases ionized calcium (H+ displaces Ca from albumin); alkalosis decreases it
- Massive transfusion with citrated blood products can cause acute ionized hypocalcemia
- Symptomatic hypocalcemia (tetany, seizures, hemodynamic instability): treat with IV calcium gluconate or calcium chloride