This test measures only the free amount of calcium in the blood, which is not bound to proteins. Your body uses it to build strong bones and teeth. Calcium is also needed for your heart and other muscles to function properly. Deficiency of calcium can cause Osteoporosis. Children who do not get enough calcium may not grow to their full potential height as adults. However, too much calcium in your blood can weaken your bones, create kidney stones and interfere with normal functioning of the heart and brain.