The Serum Calcium test is a common blood test that measures calcium levels in the blood. Calcium plays a vital role in bone health, muscle function, nerve transmission, blood clotting, and enzyme activity. This test is typically ordered to diagnose and monitor disorders like hypercalcemia (high calcium) or hypocalcemia (low calcium). Hypercalcemia may result from hyperparathyroidism, cancer, or excessive vitamin D intake, while hypocalcemia is often linked to hypoparathyroidism, vitamin D deficiency, kidney failure, or malabsorption. Since a portion of blood calcium is bound to proteins (e.g., albumin), results may require adjustment if albumin levels are abnormal. Interpretation usually involves correlating results with other tests such as PTH (parathyroid hormone), phosphorus, and vitamin D to identify the underlying cause. Venous blood sampling is used, with no special preparation except fasting in some cases.