Corrected Calcium Calculator
Albumin-corrected calcium: Ca + 0.8 × (4.0 − albumin) in mg/dL and g/dL, or Ca + 0.02 × (40 − albumin) in mmol/L and g/L. An estimate only. How it works
Use the Corrected Calcium Calculator
About the Corrected Calcium Calculator
A total calcium of 8.5 mg/dL with an albumin of 3.2 g/dL corrects to 9.14 mg/dL by the formula calcium + 0.8 × (4.0 − albumin). In SI units the sum is calcium + 0.02 × (40 − albumin in g/L), so 2.12 mmol/L with 32 g/L gives 2.28 mmol/L. Studies that compared the corrected figure with measured ionized calcium found it often disagrees, most of all when albumin is low.
Corrected calcium in mg/dL by measured calcium and albumin
| Albumin | Calcium 7.5 mg/dL | Calcium 8.0 mg/dL | Calcium 8.5 mg/dL | Calcium 9.0 mg/dL | Calcium 10.0 mg/dL |
|---|---|---|---|---|---|
| 4.0 g/dL | 7.50 | 8.00 | 8.50 | 9.00 | 10.00 |
| 3.5 g/dL | 7.90 | 8.40 | 8.90 | 9.40 | 10.40 |
| 3.0 g/dL | 8.30 | 8.80 | 9.30 | 9.80 | 10.80 |
| 2.5 g/dL | 8.70 | 9.20 | 9.70 | 10.20 | 11.20 |
| 2.0 g/dL | 9.10 | 9.60 | 10.10 | 10.60 | 11.60 |
| 1.5 g/dL | 9.50 | 10.00 | 10.50 | 11.00 | 12.00 |
Each 1 g/dL of albumin below 4.0 adds 0.8 mg/dL. Below 2.0 g/dL the page adds a note that the correction is least reliable and to ask for an ionized calcium test.
Corrected calcium in mmol/L by measured calcium and albumin
| Albumin | Calcium 1.90 mmol/L | Calcium 2.10 mmol/L | Calcium 2.30 mmol/L | Calcium 2.50 mmol/L |
|---|---|---|---|---|
| 40 g/L | 1.90 | 2.10 | 2.30 | 2.50 |
| 35 g/L | 2.00 | 2.20 | 2.40 | 2.60 |
| 30 g/L | 2.10 | 2.30 | 2.50 | 2.70 |
| 25 g/L | 2.20 | 2.40 | 2.60 | 2.80 |
| 20 g/L | 2.30 | 2.50 | 2.70 | 2.90 |
| 15 g/L | 2.40 | 2.60 | 2.80 | 3.00 |
Each 1 g/L of albumin below 40 adds 0.02 mmol/L. Below 20 g/L the page adds the same note.
Methodology
Conventional units: corrected calcium (mg/dL) = calcium + 0.8 × (4.0 − albumin in g/dL). SI units: corrected calcium (mmol/L) = calcium + 0.02 × (40 − albumin in g/L). The two agree, because 0.8 mg/dL of calcium is about 0.2 mmol/L and 1 g/dL is 10 g/L. The result prints to two decimals with the sum behind it. The page accepts calcium of 4 to 20 mg/dL (1 to 5 mmol/L) and albumin of 1 to 6 g/dL (10 to 60 g/L), and suggests switching units when a value fits the other system.
Frequently asked questions
- What is the corrected calcium formula?
- Corrected calcium = measured calcium + 0.8 × (4.0 − albumin), in mg/dL and g/dL. It comes from Payne and colleagues (BMJ, 1973), whose own abstract prints calcium − albumin + 4.0, a factor of 1; the 0.8 factor is the later form a 2021 Journal of Hospital Medicine review calls the most commonly used. With 0.8, calcium 9.0 mg/dL and albumin 2.5 g/dL correct to 10.20 mg/dL.
- Why is calcium corrected for albumin?
- About 40% of the calcium in serum is bound to albumin. When albumin is low, the total calcium on a lab report falls even though the free, ionized calcium that the body uses has not changed. The correction estimates what the total would be at an albumin of 4.0 g/dL.
- How accurate is corrected calcium?
- Often less than the uncorrected total. In a review in the Journal of Hospital Medicine (2021), a Swedish study of more than 20,000 hospital patients found the correction formulas agreed with measured ionized calcium with intraclass correlations of 0.45 to 0.81, against 0.85 for uncorrected total calcium. An Australian study of 5,500 patients found corrected values matched ionized calcium in 55% to 65% of samples and uncorrected values in 70% to 80%.
- Can I use mmol/L and g/L?
- Yes. Choose mmol/L and g/L; the page uses calcium + 0.02 × (40 − albumin). 2.30 mmol/L with an albumin of 25 g/L corrects to 2.60 mmol/L. Switching units converts the values already entered.
- What is a normal corrected calcium level?
- The Merck Manual gives normal total serum calcium as 8.8 to 10.4 mg/dL (2.20 to 2.60 mmol/L), and the corrected figure is read against the same range. Laboratories set their own limits, so the range printed on your report is the one that applies. The 9.14 mg/dL in the example sits inside the Merck range; the uncorrected 8.5 mg/dL sits below it.
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