What is the difference between Calcium and Corrected Calcium?
In our patients’ laboratory analysis printout we normally will see Calcium and Corrected Calcium values stated. So what is Calcium and Corrected Calcium…...?
Calcium is a mineral found in the largest quantity in the body and 99% is in the bones as calcium phosphate (salt). A total of 22.5 mmol of Calcium is found extra-cellular and of this 9 mmol is found in the serum.
Serum Calcium is closely regulated with normal range of Calcium (extra-cellular) of 2.2 – 2.9 mmol. The level of Serum Calcium is associated with the level of Serum Albumin. Calcium has an affinity to Albumin.
As in Chronic Kidney Disease (CKD), the Serum Albumin level is usually lower and therefore affects the reading of the Serum Calcium and does not reflect the actual Serum Calcium level.
Therefore to accurately measure the level of Serum Calcium we need to measure the free (ionized) Calcium. Ionized Calcium does not vary with the Albumin level. The normal range of ionized Calcium level is 1.1 – 1.4 mmol.
A corrected Calcium level can be calculated in situations such as CKD to present an actual representation of Calcium level in the body.
Corrected Calcium takes into consideration the abnormal level of Albumin and makes adjustment to the Calcium level as though the Albumin level is normal.
Corrected Calcium (mmol/L) =
measured total Ca (mmol/L) + 0.02 (40 - Serum Albumin [g/L]),
where 40 represents the average Albumin level in g/L
each 1 g/L decrease of Albumin, will raise 0.02 mmol/L in serum Ca
In cases of hyperalbuminemia, the level of Corrected Calcium is lower than the total Calcium.
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