EN

Corrected Calcium Calculator

This corrected calcium calculator adjusts total calcium for a low or high albumin level. Example: a calcium of 7.8 mg/dL with an albumin of 2.5 g/dL gives a corrected calcium of 9.00 mg/dL (2.25 mmol/L).

Example: Units: mg/dL and g/dL · Total calcium in mg/dL 7.8 mg/dL · Albumin in g/dL 2.5 g/dL · Correction factor: common form (0.8 or 0.02) → Result: Corrected calcium = 9.00 mg/dL (2.25 mmol/L). Source: Payne RB, Little AJ, Williams RB, Milner JR. Interpretation of serum calcium in patients with abnormal serum proteins. Br Med J 1973;4(5893):643–646 (albumin correction; original: calcium − albumin + 4.0 in mg/100 ml and g/100 ml). Updated: .

mg/dL
g/dL
My ToolboxYour inputs are saved in this browser only.

Result

Result
Corrected calcium = 9.00 mg/dL (2.25 mmol/L)
Comparison of correction factors
FormulaCorrected calcium
Common form (factor 0.8 or 0.02)9.00 mg/dL (2.25 mmol/L)
Payne 1973, original formula (factor 1.0 or 0.025)9.30 mg/dL (2.32 mmol/L)
Working
  • Corrected calcium = 7.8 + 0.8 × (4 − 2.5) = 9.00 mg/dL.
  • Conversion: 9.00 mg/dL ÷ 4.008 = 2.25 mmol/L.
Albumin correction is an approximation and does not replace a medical assessment. It is unreliable in critical illness, kidney failure and acid–base disturbances; ionised calcium is then the value that counts. Reference ranges differ between laboratories.

How it is calculated

Corrected calcium is total calcium adjusted arithmetically to an albumin of 4.0 g/dL (40 g/L). About 40% of the calcium in blood is bound to proteins, mainly albumin. When albumin is low, the measured total calcium comes out lower even though the biologically active, free fraction may be normal. The correction is meant to offset that effect.

Formula

In conventional units: corrected calcium (mg/dL) = total calcium + 0.8 × (4.0 − albumin in g/dL). In SI units: corrected calcium (mmol/L) = total calcium + 0.02 × (40 − albumin in g/L). Both go back to Payne and colleagues (British Medical Journal, 1973). The original paper states the equation as “calcium − albumin + 4.0”, i.e. with a factor of 1.0; the calculator offers both versions.

Worked example

Total calcium 7.8 mg/dL, albumin 2.5 g/dL: 7.8 + 0.8 × (4.0 − 2.5) = 7.8 + 1.2 = 9.00 mg/dL, which is 2.25 mmol/L. Payne’s original formula gives 9.30 mg/dL. In SI units: 2.00 mmol/L with an albumin of 30 g/L gives 2.00 + 0.02 × 10 = 2.20 mmol/L.

Frequently asked questions

How do you calculate corrected calcium?

Add 0.8 mg/dL to total calcium for every g/dL that albumin is below 4.0. In the example: 7.8 + 0.8 × 1.5 = 9.00 mg/dL.

When is a correction useful?

When albumin is clearly off the usual value, for instance in malnutrition, liver disease or kidney disease. With a normal albumin the formula barely changes the result.

What is the difference between the factors 0.8 and 1.0?

Payne derived a factor of 1.0 in 1973; textbooks and laboratories have settled on 0.8 (0.02 in SI units). The table shows both results side by side.

Is corrected calcium the same as ionised calcium?

No. Ionised calcium is measured directly and shows the free fraction. Corrected calcium is only an estimate based on total calcium and albumin.

Sources and legal basis

As of: · Editorial policy

Related tools