A 10-month-old exclusively breastfed infant presents with irritability, craniotabes, and wrist widening on physical examination. X-ray shows cupping and fraying of metaphyses. Serum calcium is 8.1 mg/dL, phosphorus 3.2 mg/dL, alkaline phosphatase markedly elevated, 25-OH Vitamin D level is 12 ng/mL. The single most important biochemical marker that reflects the ACTIVE SEVERITY of the disease process (not just deficiency status) is:
- A Serum 25-OH Vitamin D3 level
- B Serum alkaline phosphatase ✓
- C Urinary calcium:creatinine ratio
- D Serum 1,25-OH2 Vitamin D3 level
Explanation
Alkaline phosphatase is the most sensitive and practical marker of active rickets severity — it reflects ongoing osteoblastic activity in response to undermineralised osteoid. Levels are markedly elevated in active nutritional rickets and normalize with treatment, correlating with radiological healing. Serum 25-OH Vitamin D reflects nutritional status but can be mildly low without clinical disease. 1,25-OH2 Vitamin D is the active hormone and may paradoxically be normal or elevated in nutritional rickets due to secondary hyperparathyroidism. Urine Ca:Cr ratio is used to monitor response to treatment.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.