What is the most common cause of secondary hyperparathyroidism?

The most common cause of secondary hyperparathyroidism is chronic kidney disease (CKD). In CKD, the kidneys are unable to effectively excrete phosphate, leading to hyperphosphatemia. Elevated phosphate levels result in reduced serum calcium due to precipitation of calcium-phosphate complexes and decreased active vitamin D (calcitriol) production, which further impairs intestinal absorption of calcium.

In response to the low serum calcium levels, the parathyroid glands are stimulated to produce more parathyroid hormone (PTH), which results in secondary hyperparathyroidism. This condition is characterized by elevated PTH levels as the body attempts to compensate for the low calcium levels caused by kidney dysfunction and imbalances in phosphate and vitamin D metabolism.

While vitamin D deficiency can also lead to secondary hyperparathyroidism by reducing calcium levels, it is important to note that primary hyperparathyroidism and hypercalcemia are conditions associated with elevated calcium and increased PTH, but they typically do not lead to secondary hyperparathyroidism in the manner that chronic kidney disease does. Therefore, CKD remains the predominant cause in clinical practice.