How is serum calcium measured? what is serum calcium?

See below: Serum calcium is measured by a blood test.It is the amount of calcium in your blood stream.Calcium is an electrolyte, like sodium and pottassium. Calcium is mainly present in bones and the level in the blood is under control of several hormones. It should be in the normal range as specified by the laboratory.Low and high levels have to be investigated for various causes.