Relationship between free calcium and adjusted calcium for albumin in patients with hypoalbuminemia

Aim: Measurement of total blood calcium is an important test that reflects bone and mineral metabolism. Total calcium is adjusted for albumin in many laboratories. Besides, it should be taken into consideration that adjusting the total calcium for albumin may cause an inaccurate evaluation of free calcium. This study aims to investigate the necessity of adjusted calcium used in biochemistry laboratories and whether ionized calcium measurement provides more benefit in determining the amount of active calcium in the body. Material and Methods: We retrospectively selected 2092 samples with simultaneous measurements of free calcium, total calcium, albumin, total protein, and pH from the laboratory information system between January 2020 and June 2021. Samples with pH values outside the reference range of (7.35-7.45) and albumin values above the 4 g/dL were not included. In this study, the correlation between corrected total calcium calculated by Payne formula (usually expressed as albumin-adjusted calcium (mg/dL) =total calcium (mg/dL) + [4-albumin (g/dL)]. 0.8) and total calcium levels, total calcium and free calcium level were evaluated in hypoalbuminemia (<4 g/dL). Results: Moderate relationship was found between free calcium and total calcium (r:0,48). The adjusted calcium values calculated with the Payne formula do not reflect free calcium (r= 0,47). A significant correlation was found between adjusted calcium and total calcium (r:0.72). Discussion: Adjusted calcium application does not show a free calcium level. With the widespread use of free calcium measurement by most laboratories, the adjusted calcium application should be abandoned.