Albumin-corrected calcium (Payne formula) is a fast bedside method to adjust measured total calcium for the patient's albumin level. It detects pseudohypocalcemia from hypoalbuminemia and prevents unnecessary calcium replacement.
This guide covers why calcium binds to albumin, how the correction works in conventional and SI units, and when ionized calcium remains the gold standard.
The Payne Formula
The Payne formula adjusts total calcium toward a reference albumin of 4.0 g/dL (40 g/L):
Corrected Ca [mg/dL] = Total Ca + 0.8 × (4.0 − Albumin [g/dL])
Corrected Ca [mmol/L] = Total Ca + 0.02 × (40 − Albumin [g/L])
When albumin equals 4.0 g/dL no correction occurs — total and corrected calcium are identical.
Why Correct for Albumin?
Serum calcium exists in three fractions:
- Ionized (~50%) — physiologically active
- Albumin-bound (~40%) — biologically inactive
- Complexed to anions (~10%) — phosphate, citrate
In hypoalbuminemia (cirrhosis, nephrotic syndrome, malnutrition) measured total calcium drops without affecting ionized calcium. Without correction, hypocalcemia is misdiagnosed.
Reference Ranges
| Corrected Calcium | Classification |
|---|---|
| < 8.5 mg/dL · < 2.12 mmol/L | Hypocalcemia |
| 8.5 – 10.2 mg/dL · 2.12 – 2.55 mmol/L | Normal |
| > 10.2 mg/dL · > 2.55 mmol/L | Hypercalcemia |
When the Calculator Is Unreliable
- Severe acid-base disturbances — pH shifts directly alter calcium-albumin binding
- Multiple myeloma — paraproteins bind calcium and cause pseudohypercalcemia
- Critical care — fast dynamics, citrate anticoagulation, frequent transfusions
In these settings, ionized calcium remains the gold standard and should be measured directly.
Related Lab Values
- Anion gap — closely related albumin-correction concept in metabolic acidosis. Use the Anion Gap Calculator.
- Sodium correction in hyperglycemia — analogous corrected-electrolyte concept. Use the Sodium Correction Calculator.
- GFR (kidney function) — chronic kidney disease is a key cause of hypocalcemia. Use the GFR Calculator.
Calculate corrected calcium now
Enter total calcium and albumin — get the albumin-corrected concentration and clinical classification instantly.
Open the Corrected Calcium Calculator →FAQ
Which corrected values count as hypocalcemia?
Corrected calcium < 8.5 mg/dL (2.12 mmol/L) is hypocalcemia. Tetany, paresthesia, and cramps usually appear at much lower values — particularly with rapid drops.
Why a 0.8 correction factor?
Each 1 g/dL of albumin binds about 0.8 mg/dL of calcium. The factor comes from Payne et al. (1973) and is widely adopted clinically — though it remains empirical and population-dependent.
When should I measure ionized calcium?
In critical care, acid-base disturbances, massive transfusion (citrate), multiple myeloma, and any unclear case. Ionized calcium reflects the physiologically active fraction directly.