What is Ionized Calcium?
- Ionized calcium (iCa²⁺) is the biologically active form of calcium in the blood.
- It represents ~45-50% of total serum calcium and is not bound to proteins like albumin.
- This is the form that directly participates in physiological processes.
Why Is It Important?
More Accurate in Critical Situations
- Unlike total calcium, ionized calcium is not affected by albumin levels.
- In critically ill patients (e.g. ICU, oncology, sepsis), albumin may be low, falsely lowering total calcium levels.
- Ionized calcium gives a true picture of active calcium status.
Crucial in Pharmacologic and Clinical Scenarios
| Clinical Context | Why It Matters |
|---|---|
| Hypocalcemia / Hypercalcemia | Guides treatment decisions (IV calcium, bisphosphonates, calcitonin, etc.) |
| Oncology | Paraneoplastic syndromes (e.g. PTHrP-mediated hypercalcemia of malignancy) |
| Renal dysfunction | Altered calcium/phosphate handling; dialysis patients need accurate calcium monitoring |
| Critical care / sepsis / massive transfusion | Citrate in blood products binds calcium → ionized calcium drops |
| Drug monitoring | Drugs like cisplatin, denosumab, loop diuretics, or calcimimetics affect calcium balance |
Normal Range:
- Ionized calcium: ~1.12–1.32 mmol/L (may vary slightly by lab)
- Compare to Total calcium: ~8.5–10.5 mg/dL (requires albumin correction)
Pharmacist Role
- Monitor ionized calcium in:
- High-risk oncology patients
- Post-thyroidectomy or parathyroid surgery
- During IV bisphosphonate or denosumab therapy
- Ensure correct calcium salt is used (calcium gluconate vs calcium chloride)
- Know how to correct total calcium based on albumin (if ionized not available)