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Ionized Calcium Calculator (Hypocalcemia Correction)

Calculate estimated ionized calcium levels from total calcium, albumin, and pH to differentiate between true hypocalcemia and hypoalbuminemia.

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About

Total calcium levels reported in standard metabolic panels can be misleading. Approximately 40-45% of serum calcium binds to albumin, meaning that patients with low albumin (malnutrition, liver disease) will show artificially low total calcium despite having normal physiologically active (ionized) calcium. Conversely, acid-base disturbances affect calcium binding.

This tool calculates the estimated Ionized Calcium (iCa) by correcting for both Albumin and pH levels. It includes a clinical interpretation engine to assist in differentiating artifactual readings from true hypocalcemia requiring intervention.

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Formulas

The calculation uses the Zeisler approximation to adjust Total Calcium (Catot) based on Albumin (Alb) and pH:

iCa = Catot × [6 − 0.2 × (pH − 7.4)]Alb + 6

Note: Catot in mg/dL and Alb in g/dL.

Reference Data

Patient GroupRef Range (mmol/L)Ref Range (mg/dL)
Adults1.15 - 1.334.6 - 5.3
Children1.20 - 1.384.8 - 5.5
Neonates1.10 - 1.404.4 - 5.6

Frequently Asked Questions

This calculator is an estimation. Direct measurement via blood gas analyzer is required for critically ill patients, during massive transfusion protocols, or when pH deviates significantly ( 7.6).
Alkalosis (High pH) increases calcium binding to albumin, lowering the free ionized calcium and potentially causing tetany. Acidosis (Low pH) decreases binding, increasing ionized calcium.