Printed on 2/13/2026
For informational purposes only. This is not medical advice.
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.
Formula: Corrected Ca = Measured Ca + 0.8 × (4.0 − Albumin)
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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.
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.
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.
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).