Calcium is one of the most tightly regulated minerals in your body, essential for strong bones and teeth, proper muscle contraction (including your heartbeat), nerve signaling, and blood clotting. This test measures total calcium in your blood, which is regulated by parathyroid hormone and vitamin D working together. High calcium (hypercalcemia) can result from overactive parathyroid glands, certain cancers, excess vitamin D, or prolonged immobility, and can cause symptoms like fatigue, constipation, kidney stones, and confusion. Low calcium (hypocalcemia) can result from vitamin D deficiency, underactive parathyroid glands, kidney disease, or low magnesium, and can cause muscle cramps, tingling, or in severe cases, seizures. Because much of your calcium is bound to albumin, results are sometimes adjusted for albumin levels, or ionized calcium is checked for a more precise picture.