Which of the following reflects the expected laboratory finding in a patient with vitamin D deficiency rickets?

• A. Reduced PTH
• B. Normal PTH
• C. Elevated PTH
• D. Absent PTH

Answer: (C)

Vitamin D deficiency reduces calcium absorption from the gut, leading to low serum calcium. In response, the parathyroid glands secrete more PTH to raise calcium levels, a scenario called secondary hyperparathyroidism. This compensatory rise in PTH increases bone resorption and renal calcium reabsorption (and promotes phosphate wasting), helping to normalize calcium but often keeping phosphate low. So the expected lab finding is an elevated PTH level. A reduced, normal, or absent PTH would not fit the body's compensatory response to hypocalcemia in vitamin D deficiency.