Calcium, Ionized, Serum
This test is used to evaluate unbound (ionized) calcium. Calcium exists in serum in its ionized form or it is bound to organic anions such as phosphate and citrate, or in its most common form bound to proteins (mainly albumin). Of these, the ionized calcium is the physiologically important form. Ionized calcium is most useful clinically when trying to evaluate abnormally high or low serum calcium levels. Measurement of serum ionized calcium provides insight into the effect of total protein and albumin on serum calcium levels. This test is also useful in evaluating an individual that may have conditions that abnormally effect serum proteins. However Total Serum Calcium remains the first line test for evaluation of calcium abnormality. It should also be noted that women have greater circadian variation of ionized calcium than men.