Adjusted calcium
On results for calcium you will also usually see something called 'corrected' or 'adjusted' calcium. What is this?
In the plasma, calcium is present in 3 forms
Free (ionised) - about half of the total amount
Bound to protein - mainly albumin
Complexed - with citrate and phosphate
Only the free form is physiologically active.
Free (ionised) - about half of the total amount
Bound to protein - mainly albumin
Complexed - with citrate and phosphate
Only the free form is physiologically active.
Laboratories routinely measure the total calcium concentration which measures all 3 forms of calcium. However, changes in plasma albumin concentration will affect this total calcium concentration. If the albumin concentration falls the total amount of calcium falls because the amount of bound calcium is decreased. The unbound calcium though will remain normal. The adjusted calcium result is a calculation which determines what the total calcium would be if the albumin was normal.
The formulae for this will vary slightly from lab to lab, but as a general rule you add 0.1 mmol/L for every 5g drop in albumin from 40 g/L. So for example if the albumin = 20 g/L and the total calcium is 1.8 mmol/L then the adjusted calcium is 2.2 mmol/L. Note that once the albumin is below about 20 g/L this calculation doesn't really hold very well.
The formulae for this will vary slightly from lab to lab, but as a general rule you add 0.1 mmol/L for every 5g drop in albumin from 40 g/L. So for example if the albumin = 20 g/L and the total calcium is 1.8 mmol/L then the adjusted calcium is 2.2 mmol/L. Note that once the albumin is below about 20 g/L this calculation doesn't really hold very well.
to main calcium page
(Note that ionised calcium can be measured directly but is rarely required)
