A well-nourished 21-year-old woman presents with hypocalcemia. Her blood concentration of parathyroid hormone (PTH) is 150 pg/mL (normal 10-65 pg/mL). Her blood concentration of 1,25-dihydroxycholecalciferol is normal. Her BUN is normal. She is treated with a synthetic version of human PTH, and her blood calcium concentration normalizes. Which of the following is most likely causing her hypocalcemia?

Question

Quizplus · Accepted Answer

The elevated PTH levels with normal 1,25-dihydroxycholecalciferol and normalization of calcium with synthetic PTH suggest that the endogenous PTH is inactive, likely due to a secretion of an inactive PTH hormone molecule. PTH promotes calcium reabsorption from distal tubules of the nephron. A high PTH value is the body's normal response to a low level of calcium in the blood. The facts that the woman responds normally to synthetic human PTH and that her BUN is normal exclude kidney failure as a cause of her hypocalcemia and make the release of an inactive PTH the best choice.

A Well-Nourished 21-Year-Old Woman Presents with Hypocalcemia