Hypocalcaemia, hypoparathyroidism and vitamin D deficiency
It must be ensured that the patient does not have pseudohypocalcaemia caused by hypoalbuminaemia. When serum albumin is reduced by 10 g/l, serum/plasma calcium is reduced by 0.2 mmol/l. This explains why severe illness and malnutrition are often associated with mild asymptomatic hypocalcaemia; in these cases the concentration of serum/plasma ionized calcium remains normal and should be used for reference. Many laboratories report the albumin-corrected calcium concentration. The cause of hypocalcaemia should be determined before replacement therapy is initiated. The concentration of calcium is regulated by parathyroid hormone (PTH), vitamin D, calcitonin and phosphate. The reference values for calcium vary between different laboratories and by age (a typical reference range of plasma calcium in persons over 18 years of age is e.g. 2.15–2.51 mmol/l; the concentration of ionized calcium is approximately 50% of total calcium concentration).