Why use it

Prevents misdiagnosis of hypocalcemia in hypoalbuminemic patients. Essential in critically ill, malnourished, or cirrhotic patients. Quick bedside correction when ionized calcium is unavailable.

About

Corrected calcium adjusts the measured total serum calcium for the level of serum albumin. Since approximately 40% of circulating calcium is bound to albumin, hypoalbuminemia can cause a falsely low total calcium while the physiologically active ionized fraction remains normal. This calculator provides the corrected value to guide clinical decision-making.

When to use

Interpreting total calcium in patients with low albumin
ICU patients with hypoalbuminemia
Cirrhosis, nephrotic syndrome, or malnutrition
When ionized calcium measurement is not available

Formula

Corrected Ca (mg/dL) = Measured Ca + 0.8 × (4.0 - Albumin) Assumes normal albumin = 4.0 g/dL

Pearls & pitfalls

The correction formula is an estimate — ionized calcium is the gold standard.
For every 1 g/dL decrease in albumin below 4.0, total calcium decreases by ~0.8 mg/dL.
This correction is less reliable in critically ill patients, acid-base disturbances, and renal failure.
In alkalosis, more calcium binds to albumin, so ionized calcium drops even with normal total.
Do NOT use this correction if albumin is normal or elevated.

Next steps

If corrected calcium is abnormal, confirm with ionized calcium. Investigate underlying cause of hypocalcemia or hypercalcemia. Ionized calcium is always preferred when available.

Evidence

Payne et al. (BMJ 1973) demonstrated the linear relationship between albumin and total calcium. Widely used clinically though imperfect. Multiple studies show ionized calcium is superior, especially in ICU populations.

References

Payne RB et al. Interpretation of serum calcium in patients with abnormal serum proteins. Br Med J. 1973;4(5893):643-646. — link

Corrected Calcium

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