Useful For

Ionized (Free) Calcium (Ca⁺⁺) is the physiologically active form of calcium, which comprises approximately 45% of the total calcium in plasma.  It is essential for the contractility of smooth vascular muscle and it plays a vital part in cardiovascular function.  It is also important in muscle function, nerve function, bone formation and it is a cofactor in many cellular hormone and enzyme reactions.

Calcium is one of the most tightly controlled analytes in the body, closely controlled by the action of parathyroid hormone (PTH) and calcitonin.  Hypocalcemia can result from a deficiency of PTH, which can be caused by malabsorption of vitamin D, hypoparathyroidism, or chronic renal failure. Hypercalcemia is commonly caused by primary hyperparathyroidism and malignant disease.  In critical care situations, especially where large amounts of blood was transfused, ionized calcium levels should be monitored closely.  Transfused blood contains citrate as an anticoagulant that can bind calcium and affect its level in the blood.  Although total calcium levels may increase, ionized calcium may decrease and lead to cardiac and neuromuscular malfunction.