Clinical Information

Calcium is one of the most abundant elements in the body with about 99% of it contained in the skeleton. The remaining calcium is distributed between the various tissues and the extracellular fluids where it performs a vital role for many life-sustaining processes. Among the extra skeletal functions of calcium are involvement in blood coagulation, neuromuscular conduction, excitability of skeletal and cardiac muscle, enzyme activation, and the preservation of cell membrane integrity and permeability. In plasma, calcium exists in three physiochemical states, with approximately 50% free (ionized), 40% bound to plasma proteins (mostly albumin), and 10% complexed with small anions.

Serum calcium levels are controlled by parathyroid hormone (PTH), calcitonin, and vitamin D. An imbalance in any of these modulators leads to alterations of the body and serum calcium levels. For example, increases in serum PTH (e.g., hyperparathyroidism) or vitamin D are usually associated with hypercalcemia. Increased serum calcium levels may also be observed in multiple myeloma and other neoplastic diseases. Hypocalcemia is often seen in hypoparathyroidism, renal insufficiencies, and pancreatitis. In the case of hypoalbuminemia, decreased total calcium is seen with normal ionized calcium, due to the decrease in the protein-bound fraction of serum calcium. Urine calcium levels tend to follow the same trends as serum calcium levels. When serum calcium levels are low, more calcium is reabsorbed by the kidneys leading to decreased urine calcium levels, and vice versa.