[Albumin adjustment of total serum calcium - is it worth doing?]

Abstract

Calcium is the most abundant mineral in the human body. About 99% of calcium is deposited in the bones in the form of hydroxyapatite and only 1% is located in the intracellular and extracellular fluid. Ionized calcium, which makes up about 50% of the total amount of circulating calcium, is biologically active; the remaining percentage is bound to plasma proteins (40%, of which albumin accounts for 90%, and globulins for 10%), or is in complex with anions (10%) such as citrate, lactate, bicarbonate, phosphate. Hypo- and hypercalcemia are common conditions treated by physicians of various specialities. Primary hyperparathyroidism and malignant tumors are the most common causes of hypercalcemia, whereas hypocalcemia is most often caused by hypoparathyroidism, malabsorption, vitamin D deficiency or chronic kidney disease. The interpretation of blood calcium concentration results affects the correct diagnosis, the need for further examination, and the choice of treatment. Concentration of ionized calcium is considered a more accurate indicator of the true status of calcemia compared to the concentration of total calcium, but its measurement is difficult due to strict preanalytical and analytical requirements. In the mid-1970s, calcium adjustment equations appeared, which are widely used today. However, some studies have expressed doubts about the sufficient reliability and sensitivity of the corresponding adjustment formulas. The diagnostic accuracy of widely used correction formulas in some clinical situations is lower than the diagnostic accuracy of uncorrected total calcium. The review discusses the history of the formulas for correcting total calcium for albumin, the factors influencing the result of correction, as well as its suitability in various conditions.