Corrected Calcium Calculator
Correct total serum calcium for albumin level to reveal true calcium status.
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How to use this calculator
About 40–45% of serum calcium is bound to albumin. When albumin is low, total calcium appears falsely low. Adding 0.8 mg/dL for each 1 g/dL that albumin falls below 4 g/dL reveals the true physiological calcium level.
- 1
Enter the total serum calcium from your lab report in mg/dL.
- 2
Enter the serum albumin level from the same blood draw.
- 3
The calculator applies the standard Payne correction formula.
- 4
Use the corrected calcium value for clinical decision-making when albumin is abnormal.
Frequently asked questions
Why does albumin affect measured calcium?
Roughly 40–45% of calcium in blood is bound to albumin. When albumin is low (hypoalbuminaemia), the total calcium reading is artificially suppressed, even though the biologically active free (ionised) calcium may be normal.
What is the normal range for corrected calcium?
The normal corrected calcium range is 8.5–10.5 mg/dL (2.12–2.62 mmol/L). Values below 8.5 suggest hypocalcaemia; values above 10.5 suggest hypercalcaemia.
When should I use ionised calcium instead?
Ionised (free) calcium measurement is more accurate in critically ill patients with acid–base disturbances or very low albumin. Corrected calcium is a practical bedside estimate when ionised calcium is not available.
Does this formula apply to all patients?
The Payne formula is validated for adults. It is less accurate in patients with myeloma or major acid–base disorders. In those cases, direct ionised calcium measurement is preferred.
Corrected Calcium Calculator
Why Total Calcium Can Be Misleading
Standard lab panels report total serum calcium, which includes calcium bound to albumin and calcium carried by other proteins, in addition to free (ionised) calcium. When a patient has low albumin — which is common after surgery, liver disease, malnutrition, or chronic illness — the total calcium reading can appear low even though the physiologically active fraction is perfectly normal. The corrected calcium formula adjusts for this effect.
Clinical Significance of the Correction
Failing to correct for albumin can lead to unnecessary calcium supplementation in patients who are not truly hypocalcaemic, or missing true hypercalcaemia in patients with both high calcium and low albumin. This calculator provides the corrected value as a quick bedside tool, supplementing — but not replacing — direct ionised calcium measurement.
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