How to use this calculator
- Enter or choose units.
- Enter or choose total serum calcium.
- Enter or choose serum albumin.
- Enter or choose reference albumin.
- The corrected calcium (in the units entered) updates as you type. Use Copy result or Share to keep it.
Method
Corrected Ca (mg/dL) = Measured Ca + 0.8 × (Reference albumin − Measured albumin in g/dL); mmol/L = mg/dL ÷ 4.0078
- Measured Ca
- total serum calcium
- Albumin
- serum albumin (g/L ÷ 10 = g/dL)
- 4.0078
- mg/dL per mmol/L of calcium (molar mass 40.078 g/mol)
Worked example
- Albumin deficit = 4.0 − 2.0 = 2.0 g/dL.
- Adjustment = 0.8 × 2.0 = 1.6 mg/dL.
- Corrected calcium = 8.0 + 1.6 = 9.6 mg/dL (9.6 ÷ 4.0078 = 2.40 mmol/L).
A total calcium of 8.0 mg/dL with albumin 2.0 g/dL corrects to 9.6 mg/dL (2.40 mmol/L) by the Payne formula.
What the result means
Compare the corrected value with your laboratory’s reference range for total calcium. When the result would change management, or in critical illness, measure ionised calcium directly instead of relying on the correction.
Assumptions and limits
- The Payne correction factor of 0.8 mg/dL per g/dL of albumin applies.
- SI values are converted to mg/dL and g/dL, corrected, and converted back.
- The correction is known to be unreliable in critical illness, advanced kidney disease and acid–base disturbance; ionised calcium is preferred there.
- Different laboratories validate different correction equations; use your laboratory’s if it reports one.
Questions
What is the SI version of the formula?
It is commonly written as Ca + 0.02 × (40 − albumin in g/L) mmol/L. This calculator converts units exactly instead, and the two agree to about 0.01 mmol/L.
Is corrected calcium the same as ionised calcium?
No. Corrected calcium estimates what total calcium would be at a normal albumin; ionised calcium is the free, active fraction measured directly.
Sources
Please note: This is a general screening estimate for adults, not medical advice or a diagnosis. Talk to a qualified health professional about your health.