Corrected Calcium

Formula

Corrected Ca  =  measured Ca  +  0.8 × (4 − albumin)

For every 1 g/dL the albumin is below 4, add 0.8 to the measured calcium. The intuition: low albumin means less protein-bound calcium, so the lab reports a lower total, but the physiologically active ionized fraction is unchanged.

Why this matters clinically

• Hypoalbuminemia is common in hospitalized patients (sepsis, liver disease, malnutrition, nephrotic syndrome). A "low" total calcium in these patients usually corrects to normal.
• Avoid unneeded supplementation. Replacing calcium based on a low total in a hypoalbuminemic patient can push ionized Ca too high.
• Ionized calcium is the gold standard when available, corrected total is an estimate.

Hypocalcemia signs (Chvostek / Trousseau)

If corrected calcium is genuinely low, watch for the classic NCLEX signs:

• Chvostek sign, facial twitch when tapping the facial nerve in front of the ear.
• Trousseau sign, carpal spasm when a BP cuff is inflated above SBP for 3 minutes.
• Tetany, paresthesias around mouth/fingers, prolonged QT.

Worked example

ICU patient with sepsis: total Ca 6.8, albumin 1.8.

1. Correction: 0.8 × (4 − 1.8) = 0.8 × 2.2 = 1.76.
2. Corrected Ca: 6.8 + 1.76 = 8.56 mg/dL → low-normal, not the severe hypocalcemia the raw value suggested.
3. Reasonable plan: trend, check ionized Ca, no aggressive replacement unless symptomatic or ionized is low.