What causes pseudohypocalcemia?
Unlike true hypocalcemia (low ionized calcium), pseudohypocalcemia is defined as a normal ionized calcium, with low total serum calcium. This usually occurs in conditions associated with low serum albumin (malnutrition, nephrotic syndrome, cirrhosis, etc.). In general, the concentration of calcium falls by 0.8 mg/dL for every 1 g/dL decrease in serum albumin concentration. One of the formulas to correct serum calcium for low albumin, derived from studies in cirrhotic patients with low albumin, is:
A study of CKD patients not yet on dialysis showed that total calcium and albumin-corrected calcium failed to identify true hypocalcemia or hypercalcemia in 20% of the patients. Directly measuring the ionized calcium is preferred in this population.