In chronic kidney disease–related bone-mineral disorder, which hormone is primarily involved in secondary hyperparathyroidism?

• A. Parathyroid hormone
• B. Calcitonin
• C. Erythropoietin
• D. Aldosterone

Answer: (A)

In chronic kidney disease–related bone-mineral disorder, the body’s parathyroid glands respond to imbalances in calcium and phosphate caused by reduced kidney function, making parathyroid hormone the key player in secondary hyperparathyroidism. As the kidneys fail, phosphate clearance drops and levels rise, which tends to bind calcium and lower free calcium in the blood. At the same time, the kidneys become less able to activate vitamin D, so calcium absorption from the gut decreases. The combination of low calcium and high phosphate signals the parathyroid glands to secrete more PTH in an attempt to raise calcium levels and promote phosphate excretion. Over time, this response becomes chronically elevated, leading to secondary hyperparathyroidism. Calcitonin, erythropoietin, and aldosterone are not the primary drivers of this process.