What is the major cause of secondary hyperparathyroidism in non-dialysis CKD?

• A. Vitamin D deficiency and phosphate retention leading to secondary hyperparathyroidism
• B. Excess calcitriol production by the kidney
• C. Low phosphate intake with high calcium diet
• D. Elevated calcium absorption from the gut

Answer: (A)

In non-dialysis CKD the main problem driving secondary hyperparathyroidism is disrupted mineral metabolism from the diseased kidney: phosphate retention and impaired activation of vitamin D. As kidney function falls, the inability to excrete phosphate leads to higher serum phosphate. This excess phosphate, along with reduced activity of 1‑alpha hydroxylase, lowers the production of active vitamin D (calcitriol). Calcitriol normally promotes intestinal calcium absorption; with its deficiency, calcium absorption drops and serum calcium falls. The parathyroid glands sense this hypocalcemia and respond by increasing parathyroid hormone secretion, causing secondary hyperparathyroidism.

The other options don’t fit this setting: excess calcitriol would raise calcium and suppress PTH; very low phosphate intake with a high calcium diet would not provoke PTH elevation; and elevated gut calcium absorption would similarly tend to suppress PTH rather than stimulate it.