The ionized calcium test is a blood test used to measure the level of calcium that is free or unbound to proteins in the blood. Calcium is an essential mineral that is important for bone health, muscle function, and nerve transmission. The ionized calcium test is considered a more accurate measure of calcium levels in the blood compared to the total calcium test, which measures both bound and unbound calcium. This is because only the unbound or “free” calcium is biologically active and available for use by the body. The ionized calcium test is often used to monitor calcium levels in critically ill patients or those with kidney disease, as imbalances in ionized calcium can have serious health consequences. Abnormal results from the ionized calcium test may indicate a range of conditions such as hypocalcemia (low calcium levels) or hypercalcemia (high calcium levels), which require further evaluation and management by a healthcare provider.