A calcium blood test is a laboratory test that measures the level of calcium in the blood. Calcium is a mineral that is essential for many functions in the body, including building and maintaining strong bones, nerve function, and muscle function. The calcium blood test is often used to evaluate calcium levels in the body and to help diagnose and monitor conditions that can affect calcium levels, such as kidney disease, parathyroid disease, and bone disorders. The test is typically done by drawing a small amount of blood from a vein in the arm and sending it to a laboratory for analysis. Abnormal results on a calcium blood test may indicate a deficiency or excess of calcium in the body and may require further evaluation and treatment.