Calcium is essential for muscle contraction, nerve function, blood clotting, and bone health.

Most calcium in blood is bound to proteins (mainly albumin), but ionized calcium represents the physiologically active fraction.

Clinical uses include:

Evaluating parathyroid function and calcium metabolism.

Monitoring patients with critical illness, renal disease, or liver disease.

Assessing calcium status in hypoalbuminemia, where total calcium may be misleading.

Guiding treatment in patients with electrolyte imbalances.

More reliable than total calcium in detecting true hypocalcemia or hypercalcemia

Analyte: Ionized (free) calcium in serum/plasma (mmol/L).

Normal Range (varies by lab): ~1.12–1.32 mmol/L.

Abnormal Findings:

Low ionized calcium (hypocalcemia): Hypoparathyroidism, vitamin D deficiency, renal failure, pancreatitis, massive transfusion (citrate effect).

High ionized calcium (hypercalcemia): Hyperparathyroidism, malignancy, vitamin D intoxication, prolonged immobilization.

Clinical Use:

Provides a direct measure of physiologically active calcium.

Helps guide urgent management in ICU and emergency settings.

Supports diagnosis of parathyroid and metabolic disorders.