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Vitamin D deficiency biochemistry — MRCPCH TAS MCQ

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ModerateNutrition and metabolismVitamin D deficiency biochemistryMRCPCH TAS

A 16-month-old with delayed walking has bowed legs. Bloods show low phosphate, raised alkaline phosphatase and raised parathyroid hormone. What is the most likely diagnosis?

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Correct answer: D — Nutritional vitamin D deficiency rickets

Vitamin D deficiency rickets causes impaired mineralisation with secondary hyperparathyroidism, raised alkaline phosphatase and often low phosphate. Hypophosphatasia would be associated with low alkaline phosphatase rather than raised levels. The pearl is that biochemical interpretation is often more useful than a single calcium value.

Reference: Nelson Textbook of Pediatrics; RCPCH Theory examination syllabi; UK nutrition guidance principles