Health and clinical reference
Corrected calcium calculator (albumin-adjusted)
Albumin-adjusted total calcium in mg/dL and mmol/L, with the widely used 0.8 factor or Payne’s original 1.0 factor.
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For information only. This is a reference calculation, not medical advice or a diagnosis, and it must not be used to choose or adjust medicine doses. Discuss any result or health decision with a qualified clinician.
Result
Method and limits
About half of serum calcium is bound to albumin, so total calcium falls when albumin is low even if the active, ionized calcium is normal. The adjustment adds back a fixed amount per g/dL of albumin below a reference value.
Corrected Ca (mg/dL) = Ca + factor × (reference albumin − albumin) (albumin in g/dL)
Payne et al. (1973): adjusted calcium = calcium − albumin + 4.0 (mg/100 mL, g/100 mL)
Calcium: 1 mmol/L = 4.008 mg/dLAssumptions and limits
- Correction formulas often misclassify calcium status, especially in kidney disease and critical illness; directly measured ionized calcium is preferred when it matters.
- Many laboratories derive their own adjustment equation; use theirs when it is reported.
Worked example
Calcium 8.0 mg/dL with albumin 2.5 g/dL: 8.0 + 0.8 × (4.0 − 2.5) = 9.2 mg/dL (2.30 mmol/L). With Payne’s factor of 1.0: 9.5 mg/dL.
References
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