Why correct calcium for albumin?

About 40% of total serum calcium is bound to albumin. When albumin is low (common in hospitalized patients, liver disease, malnutrition), measured total calcium may appear falsely low even when ionized (free) calcium is normal. Correcting gives a better estimate of the true calcium status.

What is the correction formula?

Corrected Ca = Measured Ca + 0.8 × (4.0 − Albumin). For example, if calcium is 8.0 mg/dL and albumin is 2.0 g/dL: corrected Ca = 8.0 + 0.8 × (4.0 − 2.0) = 9.6 mg/dL.

When should I use ionized calcium instead?

Ionized (free) calcium is the gold standard and should be used when available, especially in critically ill patients, those with acid-base disturbances, or when albumin correction is unreliable (e.g., massive transfusion, severe sepsis). The correction formula is an approximation.

What is a normal corrected calcium level?

Normal corrected calcium is 8.5–10.5 mg/dL. Below 8.5 suggests hypocalcemia (evaluate PTH, vitamin D, magnesium). Above 10.5 suggests hypercalcemia (most commonly hyperparathyroidism or malignancy).

Online Medical Tools — Corrected Calcium

Printed on 2/13/2026

For informational purposes only. This is not medical advice.

Corrected Calcium

About 40% of serum calcium is bound to albumin, so low albumin levels can make total calcium appear falsely normal or low. The corrected calcium formula adjusts the measured total calcium upward by 0.8 mg/dL for each 1 g/dL decrease in albumin below 4.0. This gives a more accurate picture of the physiologically active calcium level, especially in hospitalized or malnourished patients.

Compare with Anion Gap

Formula: Corrected Ca = Measured Ca + 0.8 × (4.0 − Albumin)

Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.