Calcium Total & Ionized

A Serum Calcium test measures the levels of calcium in the body. Calcium is the most abundant mineral in the body, and the majority of it is present in the bones and teeth, and the remaining portion (around 1%) is found in the blood. It is normally present in two forms in blood in about equal amounts, namely "bound calcium", which is attached to proteins in the blood, and "free calcium or ionized calcium", which is not attached to any protein. 

A Serum Calcium test cannot be used to check for a lack of calcium in your diet or osteoporosis (loss of calcium from bones) as the body can have normal calcium levels even in case of dietary deficiency of calcium. Moreover, the body can normalize mild calcium deficiency by releasing the calcium stored in bones.