How are calcium levels affected by changes in albumin concentration? How can the affect of albumin levels be accounted for?

  • Total calcium levels are generally dependent on the level of plasma albumin
  • With reduced serum albumin proportionally less calcium is bound
  • This results in a lower measured total plasma calcium
  • A corrective formula (Payne’s formula) is commonly applied to account for albumin concentrations when considering the measured total calcium levels
  • A correction factor of 0.02 mmol/L is added to the measured calcium level for every 1 g/L of albumin below a value of 40 g/L)
  • Results in the formula:

Corrected Ca2+ = measured Ca2+ + 0.02 x (40 – serum albumin)

Corrected Calcium

  • For example, if the measured total plasma calcium is 1.876 mmol/L and plasma albumin is 26 g/L:
Corrected Ca2+ = 1.83 + 0.02 x (40 – 26)
= 1.83 + 0.28
= 2.11 mmol/L

Worked Example