Which laboratory pattern is typical of vitamin D deficiency?

Which laboratory pattern is typical of vitamin D deficiency?

• A. Calcium high; Phosphate high; PTH high
• B. Calcium low; Phosphate high; PTH normal
• C. Calcium normal; Phosphate low; PTH high
• D. Calcium low; Phosphate low; PTH high

Answer: (D)

When vitamin D is deficient, the gut absorbs less calcium and phosphate. This lowers serum calcium (often low or low-normal) and phosphate as well. The drop in calcium stimulates the parathyroid glands to release more parathyroid hormone, causing secondary hyperparathyroidism. PTH then raises calcium levels by promoting bone resorption and renal calcium reabsorption, but it also increases phosphate excretion in the kidney, keeping serum phosphate low. So the typical pattern is low calcium, low phosphate, and high PTH.

When vitamin D is deficient, the gut absorbs less calcium and phosphate. This lowers serum calcium (often low or low-normal) and phosphate as well. The drop in calcium stimulates the parathyroid glands to release more parathyroid hormone, causing secondary hyperparathyroidism. PTH then raises calcium levels by promoting bone resorption and renal calcium reabsorption, but it also increases phosphate excretion in the kidney, keeping serum phosphate low. So the typical pattern is low calcium, low phosphate, and high PTH.