MLT GlobeCalcium, ionized
Electrolytes · also called iCa, Free calcium, Ca²⁺
What it measures
Ionized calcium is the physiologically active, unbound fraction. It is preferred over total calcium in critically ill patients, during surgery and transfusion, and when albumin or pH is abnormal.
Specimen and preparation
- Specimen: Heparinised whole blood (balanced heparin) or anaerobic serum
- Tube: Green top
- Preparation: Collect anaerobically with minimal tourniquet; analyse promptly. Loss of CO₂ raises pH and lowers ionized calcium.
Reference range
| Group | Range |
|---|---|
| Adult | 4.6–5.3 (1.15–1.32) mg/dL (mmol/L) |
Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.
Causes of high values
- Primary hyperparathyroidism
- Malignancy
- Acidosis
- Vitamin D toxicity
Causes of low values
- Massive citrate transfusion
- Sepsis and critical illness
- Alkalosis (including hyperventilation)
- Hypoparathyroidism
- Acute pancreatitis
Method
Ion-selective electrode on a blood gas or electrolyte analyser
Good to know
Critical values are usually <0.8 or >1.6 mmol/L.
Related tests
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