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Bone Metabolism

Building Strong Bones

 

Calcium and phosphorous are the most abundant minerals found in the body, and the majority of both minerals are found in the skeletal system. Calcium regulation is required for many basic body functions, such as cell function, bone structure, blood clotting, and neural transmission. Insufficient calcium or loss of calcium is called hypocalcemia, whereas too much calcium in the blood, often a result of malignancy or primary hyperthyroidism, is called hypercalcemia. The body regulates calcium through the parathyroid hormone (PTH) and vitamin D, and, to a lesser extent, calcitonin.

Enhancing Calcium Absorption with PTH and Vitamin D

PTH Vitamin D
  • Enhances calcium absorption in the intestines by stimulating the renal synthesis of 1.25(OH)2D
  • Increases the amount of calcium in the blood through the release of PTH and the removal of calcium from the bone
  • Decreases the amount of calcium by releasing less PTH
  • Helps to form and maintain strong and healthy bones by increasing the amount of dietary calcium absorbed by the intestines
  • Stops the parathyroid gland from secreting parathyroid hormone, which would increase levels of calcium in the blood
  • Protects against osteoporosis, cancer, and hypertension

Clinical Utility of Calcium and PTH for Differential Diagnosis

Physicians use the combination of calcium and PTH measurements to aid in the differential diagnosis of several diseases.

Disease Calcium Level PTH Level Description
Hyperparathyroidism High High Usually caused by a benign tumor on the parathyroid gland. Surgical removal of tumor is confirmed using intraoperative PTH.1
Hypoparathyroidism Normal Low Cause of hypocalcemia since the thyroid gland is sometimes damaged during surgery and unable to produce PTH.2
Hypercalcemia of malignancy High Low High levels of calcium caused by bone metastasis that destroy the bone and release calcium into the bloodstream.3
Secondary hyperparathyroidism in renal disease Low High Renal patients often have low circulating calcium levels which cause PTH levels to rise. Dietary calcium supplements help the PTH levels return to normal. Persistently elevated PTH levels in renal patients can lead to bone disease, causing muscle pain, bone deformity and increased incidence of fracture.1

1 National Endocrine and Metabolic Disease Information Service, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), NIH

2 Medline Plus, U.S. National Library of Medicine and the National Institute of Health

3 National Cancer Institute

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