Normal ionized calcium in paediatrics
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Based on the textbook content gathered, here is a comprehensive summary:
Normal Ionized Calcium in Paediatrics
Reference Ranges
| Population | Ionized (Free) Calcium | Total Calcium |
|---|---|---|
| Adults (reference) | 1.15–1.33 mmol/L (4.6–5.3 mg/dL) | 8.5–10.5 mg/dL (2.12–2.62 mmol/L) |
| Neonates / Infants / Children | Slightly higher than adults; age-specific intervals apply | Higher upper limits in early life |
For detailed age-stratified paediatric reference intervals, the CALIPER (Canadian Laboratory Initiative on Paediatric Reference Intervals) study provides the most authoritative values and is referenced directly by the Tietz Textbook of Laboratory Medicine (7th ed.) as the gold-standard paediatric dataset.
Key Points
- Ionized (free) calcium represents ~45% of total serum calcium. It is the physiologically active fraction, tightly regulated by PTH and vitamin D.
- The remaining calcium is protein-bound (~45%, mainly to albumin) and complexed to anions (~10%, e.g., citrate, phosphate).
- Ionized calcium values are pH-dependent: alkalosis decreases it (more protein binding), acidosis increases it. Results should always be reported alongside pH, or corrected to pH 7.4.
- Neonates are particularly vulnerable to hypocalcemia (especially preterm infants and after large citrate-containing blood product transfusions). Ionized calcium monitoring is considered essential in critically ill neonates and children.
- In neonates, ionized calcium <1.0 mmol/L and in infants/children <1.1 mmol/L is generally considered hypocalcaemic, though exact thresholds vary by institution.
Why Ionized > Total Calcium in Paediatrics?
Hypoalbuminaemia (common in sick children) can make total calcium falsely normal while ionized calcium is actually low. Measuring ionized calcium directly bypasses this pitfall and is the preferred measurement in:
- Neonates and critically ill children
- Post-cardiac surgery patients
- Patients receiving massive transfusions
Practical Reference Values Commonly Used
| Age Group | Ionized Calcium (mmol/L) |
|---|---|
| Neonates (0–1 month) | 1.10–1.38 |
| Infants (1–12 months) | 1.20–1.40 |
| Children (1–18 years) | 1.15–1.35 |
| Adults | 1.15–1.33 |
These figures are representative; always use your local laboratory's reference range as instrument-specific calibration affects results.
Sources: Tietz Textbook of Laboratory Medicine, 7th ed. | Textbook of Family Medicine, 9th ed. | Morgan & Mikhail's Clinical Anesthesiology, 7th ed.
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