Notes & Sources

• Roughly 40% of serum calcium is albumin-bound. In hypoalbuminaemia, total calcium understates the physiologically active fraction — correction estimates what the total would be at a normal albumin of 4.0 g/dL.
• The correction is an approximation only. Where the result changes management — and in critical illness, renal failure or acid–base disturbance — measure ionised calcium instead.
• Reference range used here: 8.5–10.5 mg/dL. Adjust to your own laboratory’s range.