Corrected Calcium for Albumin

Calcium correction is a calculation used in clinical medicine to estimate the true level of calcium in the blood, adjusting the measured total calcium value based on the patient's albumin concentration. In the blood, a significant portion of calcium (approximately 40-50%) circulates bound to proteins, primarily albumin, while the remainder is free (ionized) or complexed with anions. Only the ionized calcium is biologically active and physiologically important for functions such as muscle contraction, nerve transmission, and blood clotting. When a patient has low albumin levels (hypoalbuminemia), as seen in liver disease, malnutrition, or critical illness, there are fewer binding sites for calcium, causing the measured *total* calcium level to appear falsely low (pseudohypocalcemia), even if the *ionized* calcium level is normal and physiologically adequate. Conversely, high albumin levels (hyperalbuminemia) can falsely elevate the total calcium measurement. To avoid misdiagnosis and inappropriate treatment, the corrected calcium is calculated, which provides an estimate of what the total calcium would be if the albumin level were normal (typically 4.0 g/dL or 40 g/L). The most common formula used for this adjustment is: Corrected Calcium (mg/dL) = Measured Total Calcium (mg/dL) + 0.8 * (4.0 - Patient's Albumin g/dL). Despite its wide use, this correction is an estimate and has limitations, not being as accurate as the direct measurement of ionized calcium, which is the gold standard, especially in critically ill patients or those with acid-base disturbances.