Which of the following is NOT a typical biochemical finding in Vitamin D deficient rickets?

• A. Low calcium
• B. Low phosphorus
• C. High alkaline phosphatase
• D. Low alkaline phosphatase

Answer: (D)

Vitamin D deficiency causing rickets leads to poor mineralization of bone because calcium and phosphate are not adequately absorbed. The resulting low calcium triggers secondary hyperparathyroidism, which increases bone turnover and phosphate wasting, keeping phosphate levels low. The osteoblasts respond to defective mineralization by ramping up activity, which raises alkaline phosphatase levels. So high alkaline phosphatase is a typical finding. A low alkaline phosphatase would not fit this pattern and is more typical of hypophosphatasia, a different disorder. Therefore, the statement describing low alkaline phosphatase is not typical of vitamin D–deficient rickets, while low calcium, low phosphate, and high alkaline phosphatase are.