What is the standard correction factor used in the adjusted calcium formula for hypoalbuminemia?

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The main idea is that total calcium falls when albumin is low because calcium binds to albumin. To estimate what the calcium would be if albumin were normal, a correction is applied using a standard factor of 0.8 mg/dL per 1 g/dL decrease in albumin from the normal level (about 4 g/dL).

So, the corrected calcium is calculated as: measured total calcium + 0.8 × (4 − albumin in g/dL). For example, if albumin is 3 g/dL and the measured calcium is 9.0 mg/dL, the correction adds 0.8 × (4 − 3) = 0.8, giving a corrected calcium of 9.8 mg/dL. This adjustment reflects the amount of calcium that would be free if albumin were at normal concentration.

Therefore, the standard correction factor is 0.8 mg/dL per g/dL of albumin.