Total and ionized calcium in serum
Reference values of total calcium concentration in blood serum are 2.15-2.5 mmol / l or 8.6-10 mg%;ionized calcium is 1.15-1.27 mmol / l.
The physiological significance of calcium is to reduce the ability of tissue colloids to bind water, reduce the permeability of tissue membranes, participate in the construction of the skeleton and the system of hemostasis, as well as in neuromuscular activity. It has the ability to accumulate in places of tissue damage by various pathological processes. Approximately 99% of the calcium is in the bones, the rest is mainly in the extracellular fluid( almost exclusively in the blood serum).Approximately half of the serum calcium circulates in the ionized( free) form, the other half in the complex, mainly with albumin( 40%) and in the form of salts - phosphates, citrate( 9%).The change in serum albumin, especially hypo-albuminemia, affects the total calcium concentration, without affecting a clinically more important indicator - the concentration of ionized calcium. It is possible to calculate the "corrected" total calcium concentration in the serum with hypoalbuminemia according to the formula: Ca( corrected) = Ca( measured) + 0.02x( 40-albumin).Calcium, fixed in bone tissue, is in interaction with the ions of blood serum. Acting as a buffer system, the deposited calcium prevents fluctuations in its serum content in large ranges.
Calcium metabolism regulates parathyroid hormone( PTH), cal-cytonin and vitamin D derivatives. PTH increases calcium concentration in the serum, enhancing its leaching out of the bones, reabsorption in the kidneys and stimulating the conversion of vitamin D into the active metabolite calcitriol. PTH also enhances the excretion of phosphate by the kidneys. The level of calcium in the blood regulates the secretion of PTH by the mechanism of negative feedback: hypocalcemia stimulates, and hypercalcemia suppresses the release of PTH.Calcitonin is a physiological antagonist of PTH, it stimulates the excretion of calcium by the kidneys. Metabolites of vitamin D stimulate the absorption of calcium and phosphate in the intestine.
The calcium content in the blood serum changes with dysfunction of parasitic and thyroid glands, neoplasms of different localization, especially when metastasized in the bone, with renal failure. Secondary involvement of calcium in the pathological process takes place in the pathology of the gastrointestinal tract. Often hypo- and hypercalcemia may be the primary manifestation of the pathological process.