Hypercalcemia

Excerpt

Calcium is the most abundant cation in the human body and plays an integral role in neural transmission, enzyme activity, myocardial function, coagulation, and other cellular functions. Most of the calcium is found in the bones as calcium phosphate, whereas a small percentage is found in cells and extracellular fluids. In the serum, about 45% of calcium is bound to proteins, 45% exists as the active form of free or ionized calcium, and 10% is bound to anions. Normal calcium levels range from approximately 8.9 to 10.1 mg/dL, but this number can vary depending on the laboratory. Serum calcium levels fluctuate based on serum albumin levels, as a large percentage of calcium is bound to albumin. Therefore, calcium levels must be adjusted based on albumin levels. Hydrogen ions also bind to circulating albumin, so both acidosis and alkalosis can affect serum calcium levels. For example, increased hydrogen ions in acidosis take up additional binding sites on albumin, leading to increased free calcium levels. Thus, calcium levels should also be adjusted for serum pH.