What is the primary cause of hypercalcemia in chronic renal insufficiency?

The primary cause of hypercalcemia in chronic renal insufficiency is secondary hyperparathyroidism. In patients with chronic renal failure, the kidneys are unable to adequately excrete phosphate, leading to hyperphosphatemia. This, in turn, results in a decrease in serum calcium levels due to the inverse relationship between calcium and phosphate. The parathyroid glands respond to the low calcium levels by increasing the secretion of parathyroid hormone (PTH), attempting to mobilize calcium from bone, increase intestinal absorption of calcium (in conjunction with vitamin D), and enhance renal tubular reabsorption of calcium.

Over time, the continuous stimulation of the parathyroid glands can lead to hyperparathyroidism, where PTH levels remain elevated. This prolonged state of elevated PTH can contribute to alterations in bone metabolism and can be associated with increased calcium release from bone into the bloodstream, resulting in hypercalcemia, particularly in the latter stages of renal failure when other compensatory mechanisms are exhausted.

Other options like renal osteodystrophy refer to bone disease associated with renal failure, primarily involving altered mineral metabolism but not a direct cause of hypercalcemia. Vitamin D deficiency typically leads to hypocalcemia, and hypoparathyroidism results in low levels