Calcium Disturbances

How to Cite This Chapter: Srivaratharajah K, Merali Z, Panju M, Mathew A, Kokot F, Franek E, Drabczyk R. Calcium Disturbances. McMaster Textbook of Internal Medicine. Kraków: Medycyna Praktyczna. Accessed April 15, 2024.
Last Updated: December 15, 2021
Last Reviewed: December 15, 2021
Chapter Information

Physiologic BackgroundTop

Total body calcium content is 20 to 25 g/kg lean body weight, which accounts for ~1.4% to 1.6% of total body weight. The normal range of serum [Ca2+] is 2.25 to 2.62 mmol/L (9-10.5 mg/dL). Slight interlaboratory variations may exist.

In the body, 98% of calcium is located in bones. The remaining 1% to 2% can undergo rapid mobilization; half of this is ionized (biologically active) calcium, and the rest is protein-bound (mainly albumin-bound). Alkalosis increases binding of calcium to proteins, thus decreasing the levels of ionized calcium; acidosis has the opposite effect.

Daily dietary calcium intake is ~1 g; ~30% of this is absorbed. The gastrointestinal absorption of calcium is increased by 1,25(OH)­2D3 and parathyroid hormone­­—mediated by 1,25(OH)2D3—and decreased by oxalate, phosphate, and fatty acids as a result of binding in the intestinal lumen. From 98% to 99% of calcium filtrated in the glomeruli undergoes reabsorption in the renal tubules. Daily urinary calcium excretion is 3 to 5 mmol.

Intracellular and extracellular calcium are important in many enzymatic reactions and play a regulatory role in vital body functions (eg, blood coagulation, signal transmission in the nervous system, muscle contraction).

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