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Regulation of calcium and phosphate balance

Jonathan Hogan, MD
Stanley Goldfarb, MD
Section Editor
Richard H Sterns, MD
Deputy Editor
Albert Q Lam, MD


The maintenance of calcium and phosphate homeostasis involves intestinal, bone, and renal handling of these ions.

Within the plasma, calcium circulates in different forms. Of the plasma calcium, roughly 40 percent is bound to albumin, 15 percent is complexed with citrate, sulfate, or phosphate, and 45 percent exists as the physiologically important ionized (or free) calcium. As routinely measured in the laboratory, the plasma calcium concentration includes all of the calcium in the plasma (free and bound). In general, measuring the total plasma calcium concentration is sufficient since changes in this parameter are usually associated with parallel changes in the ionized concentration. Exceptions to this commonly occur in patients with hypoalbuminemia, acid-base disorders, and chronic kidney disease. Issues surrounding the measurement of total and ionized calcium are presented elsewhere in detail. (See "Relation between total and ionized serum calcium concentrations".)

In comparison to calcium, plasma phosphorus exists in both organic and inorganic forms, including phospholipids, ester phosphates, and inorganic phosphates. Inorganic phosphates are completely ionized, circulating primarily as HPO42- or H2PO4- in a ratio of 4:1 at a plasma pH of 7.40.

Only a small fraction of the total body calcium and phosphate is located in the plasma. However, it is the plasma concentrations of ionized calcium and inorganic phosphate that are under hormonal control. Calcium balance is mediated primarily by parathyroid hormone (PTH) and calcitriol (1,25-dihydroxyvitamin D), which affect intestinal absorption, bone formation and resorption, and urinary excretion [1-4]. Phosphorous balance is also primarily regulated by PTH but may also respond to fibroblast growth factor 23 (FGF-23) and its cofactor, Klotho, which together and separately promote renal excretion of phosphorous [5,6]. The physiologic roles of other hormones (such as calcitonin and estrogens) in the regulation of calcium and phosphate balance are incompletely understood [7].


Gastrointestinal calcium handling — Dietary calcium is absorbed by two mechanisms [7]:


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Literature review current through: Sep 2016. | This topic last updated: Aug 29, 2016.
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