Estimation of Total Calcium in Serum and Urine
Calcium is the most abundant mineral cation in the body which contains 1–1.5 kg of total body weight in the adults. Over 99% is present in the bones and teeth. A small fraction is also present outside the skeletal tissue and performs wide variety of functions. Most of blood calcium is present in plasma. There is almost no calcium in red blood cells and other intracellular fluid. About 50% of total plasma calcium exists in ionized form which is functionally most active. About 40% of plasma calcium is protein bound, and 10% is complexed with citrate, organic acid, or bicarbonates. About 90% of protein-bound calcium is associated with albumin, and the remaining 10% is associated with globulins. Ionized and citrate-bound calcium is diffusible from blood to the tissues, while protein bound is nondiffusible. In the laboratory, all three fractions of calcium are measured together.