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Calcium Corrected Albumin

Calcium occurs in plasma in the following forms:

• 45% is protein bound, predominantly to albumin, and is biologically inert
• 50% is free or ionized calcium and is metabolically active
• 5% is complexed with citrate and is also biologically inert.

. It can be measured as total calcium, ionised calcium, or corrected calcium (in which total calcium is corrected, usually in relation to the patient’s albumin level). When the serum albumin level is low a higher percentage of total serum calcium will be free and metabolically active. Therefore, even though the total serum calcium may be low the patient may not be metabolically hypocalcemic. Since the ionized serum calcium level is a direct measure of the amount of metabolically active serum calcium no other calculation need be done when it is available. Unfortunately, this test is not always easily available. Therefore, corrected calcium is used to obtain a reasonable estimate of the free calcium. However, in cases of multiple myeloma it is recommended that an ionized serum calcium level be done if at all possible, as a significant percentage of the total serum calcium may be bound to myeloma proteins.

(ref:  http://www.palliative.org/PC/ClinicalInfo/NursesNotes/SerumCalcium.html )

         Calculation

        Calcium (corrected, mmol/L) = Calcium (measured, mmol/L) + {(40 - albumin(g/L)) x 0.02}