Question on albumin and Calcium

[cheruka]

So, when we measure serum calcium, if albumin is low, the measured calcium may be low and inaccurate. It is the ionized calcium that is regulated by the body, not the protein bound. So, why does the measured value give you the calcium bound to albumin?
There seems to be a similar association between ceruloplasmin and serum copper.

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[Raryn]

So, when we measure serum calcium, if albumin is low, the measured calcium may be low and inaccurate. It is the ionized calcium that is regulated by the body, not the protein bound. So, why does the measured value give you the calcium bound to albumin?
There seems to be a similar association between ceruloplasmin and serum copper.

The measured value is the total blood Calcium. The reason we measure the total rather than the ionized calcium is simply because the assay is cheaper. If the albumin is low, you can calculate a correcting factor for that by adding 0.8 to the total blood calcium for every point the albumin is below 4.

You can also order an ionized calcium level, but it's rather expensive.