Which statement is true about serum calcium measurement?

Which statement is true about serum calcium measurement?

• A. Serum calcium equals ionized calcium only
• B. Serum calcium equals protein-bound plus free
• C. Serum calcium equals bone calcium only
• D. Serum calcium equals free calcium only

Answer: (B)

Serum calcium measurement reflects the total amount of calcium present in the blood, which consists mainly of calcium bound to proteins (mostly albumin) and calcium in the free (ionized) form. In routine practice, the total calcium reported by the lab is effectively the sum of these protein-bound and free calcium components, with a small portion also existing as calcium complexed with anions. That’s why the statement describing serum calcium as protein-bound plus free is the best description of what is measured. The other statements aren’t accurate because serum calcium is not limited to just ionized calcium, not limited to bone calcium, and not limited to the free form alone.

Serum calcium measurement reflects the total amount of calcium present in the blood, which consists mainly of calcium bound to proteins (mostly albumin) and calcium in the free (ionized) form. In routine practice, the total calcium reported by the lab is effectively the sum of these protein-bound and free calcium components, with a small portion also existing as calcium complexed with anions. That’s why the statement describing serum calcium as protein-bound plus free is the best description of what is measured. The other statements aren’t accurate because serum calcium is not limited to just ionized calcium, not limited to bone calcium, and not limited to the free form alone.