What does the Ionized Calcium test measure?

Why is Ionized Calcium measured?

Ionised calcium is the definitive measure of calcium status when protein binding is altered or acid–base disturbances are present. Total calcium can be misleading in hypoalbuminaemia, critical illness, and pH shifts, whereas ionised calcium reflects true availability and governs symptoms. It is the test of choice for diagnosing true hypocalcaemia and hypercalcaemia in the intensive care unit, operating theatre, and any setting where albumin or pH is abnormal, and it is essential for guiding acute intervention when neuromuscular or cardiac manifestations are present.

Reference ranges

Standard reference

Approximately 1.16–1.32 mmol/L (4.6–5.3 mg/dL), pH- and temperature-corrected.

Functional medicine optimal

Physiological homeostasis is narrow; values outside the laboratory reference interval nearly always warrant investigation.

Units

mmol/L, mg/dL

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.