Description
Blood ionised calcium is usually maintained within a tight range of 1 1.5 mmol/l (approximating to a total blood calcium of 2.2 2.6 mmol/l) by the action of parathyroid hormone, and subsequently the active vitamin D metabolite 1,25 dihydroxy vitamin D, on gastrointestinal calcium absorption, renal tubular reabsorption of calcium and bone resorption. Total blood calcium is affected by blood protein levels but most correction values produce results that relate poorly to directly measured ionised calcium and, therefore, serve no useful purpose in clinical care.
