A clinician suspects inadequate vitamin D synthesis in an elderly, institutionalized patient with fractures despite adequate calcium intake. Which laboratory pattern most supports vitamin D deficiency as the primary cause?

• A. High serum 25‑OH D, high calcium, low PTH, and low urinary calcium excretion indicating vitamin D intoxication as the cause of fractures.
• B. Low serum 25‑OH D, low or normal serum calcium, low serum phosphate, and elevated parathyroid hormone (secondary hyperparathyroidism) consistent with insufficient vitamin D-mediated mineral absorption.
• C. Low 25‑OH D with suppressed PTH due to pituitary failure indicating that osteoporosis is unrelated to vitamin D status and driven by endocrine malignancy.
• D. Normal 25‑OH D with markedly prolonged PT and PTT indicating vitamin K deficiency resulting in fragile bones and fractures.

Answer: (B)