Ionized calcium is the biologically active, free form of calcium that is not bound to proteins in the blood and is essential for numerous bodily functions including muscle contraction, nerve transmission, blood clotting, and bone formation. This test measures the amount of free calcium ions in the blood, providing a more accurate assessment of calcium status than total calcium measurements. Ionized calcium levels are not affected by changes in blood protein levels, making this test particularly useful when evaluating patients with conditions that alter protein levels, such as liver disease, kidney disease, or multiple myeloma. Abnormal ionized calcium levels can cause serious symptoms including muscle weakness, heart rhythm problems, confusion, and in severe cases, coma or death. This test is commonly ordered when other calcium tests show conflicting results or when a more precise evaluation of calcium metabolism is needed.