Acid-Base & ElectrolytesEvidence-Based Golden Standard
Corrected Calcium for Hypoalbuminemia (Payne Formula)
Estimates true physiological ionized calcium fraction when total calcium is skewed by hypoalbuminemia or hyperalbuminemia.
In mg/dL: Corrected Ca = Total Ca + 0.8 × (4.0 - Albumin [g/dL])
In mmol/L: Corrected Ca = Total Ca + 0.02 × (40 - Albumin [g/L])
Published Clinical Benchmark Cases
Clinical Parameters & Inputs
Unit: mg/dL
mg/dL
Unit: g/dL
g/dL
Computed OutputPseudohypocalcemia (Normocalcemic)
9.2mg/dL
Diagnostic Interpretation
Corrected Calcium (9.2 mg/dL) is within normal limits (8.5 – 10.5 mg/dL). The apparent low total calcium was a laboratory artifact of hypoalbuminemia (pseudohypocalcemia). Active physiological ionized calcium is preserved.
Calculation Breakdown
Payne Adjustment Calculation
7.6 + 0.8 × (4 - 2) =9.2 mg/dL
Clinical Decision Pearls
- Approximately 40-50% of circulating total calcium is bound to albumin. Only the unbound ionized calcium is biologically active.
- When clinical suspicion is high or critical decisions depend on calcium (e.g. cardiac arrhythmias, severe sepsis, blood transfusion), always measure whole-blood ionized calcium directly rather than relying solely on mathematical correction formulas.
Limitations & Confounders
- Payne formula frequently overestimates or underestimates ionized calcium in end-stage renal disease (ESRD), critically ill patients, and acid-base disturbances (acidosis decreases albumin binding, increasing ionized calcium).
Evidence & Citations
- Payne RB, et al. Interpretation of serum calcium in patients with abnormal serum proteins. Br Med J. 1973;4(5893):643-646.