A 18-month-old child from rural India presents with bleeding gums, poor wound healing, and petechial rash over lower limbs. Mother reports the child has been exclusively on boiled milk and rice for the past 6 months. Which investigation would be most appropriate to confirm the suspected diagnosis?

## Clinical Diagnosis: Vitamin C Deficiency (Scurvy) ### Presentation Analysis The clinical triad of bleeding gums, poor wound healing, and petechiae in a toddler on a diet devoid of fresh fruits and vegetables is pathognomonic for vitamin C deficiency (scurvy). **Key Point:** Vitamin C is essential for collagen cross-linking and hydroxylation of proline and lysine residues. Without it, collagen becomes unstable, leading to fragile blood vessels and poor wound healing. ### Investigation of Choice **High-Yield:** Serum ascorbic acid level is the gold standard confirmatory test for vitamin C deficiency. Normal levels are >0.6 mg/dL; deficiency is confirmed at <0.2 mg/dL. ### Why Serum Ascorbic Acid? 1. **Specificity:** Directly measures the deficient nutrient 2. **Diagnostic accuracy:** Correlates with tissue stores and clinical severity 3. **Quantitative:** Allows grading of deficiency (mild, moderate, severe) 4. **Cost-effective:** Simple blood test, widely available ### Pathophysiology of Scurvy ```mermaid flowchart TD A[Vitamin C Deficiency]:::outcome --> B[Impaired Collagen Synthesis] B --> C[Defective Collagen Cross-linking] C --> D[Fragile Blood Vessels]:::outcome C --> E[Poor Wound Healing]:::outcome D --> F[Bleeding Gums & Petechiae]:::outcome E --> G[Delayed Fracture Healing]:::outcome ``` ### Clinical Features of Scurvy | Feature | Pathophysiology | |---------|------------------| | Bleeding gums | Fragile gingival capillaries | | Petechiae/ecchymosis | Defective vessel walls | | Poor wound healing | Impaired collagen deposition | | Bone pain (scorbutic rosary) | Subperiosteal hemorrhage | | Anemia | Chronic blood loss + iron malabsorption | | Follicular hyperkeratosis | Keratinization defect | **Clinical Pearl:** The "corkscrew hairs" and follicular hyperkeratosis seen in scurvy are due to defective keratin synthesis, not just vitamin C deficiency alone — the combination with poor wound healing makes scurvy distinctive. ### Differential Diagnosis Considerations **Mnemonic: BLEED** — causes of bleeding in children: - **B**leeding disorder (hemophilia, von Willebrand) — PT/aPTT abnormal - **L**eukemia — CBC shows blasts - **E**ndocrine (scurvy) — **ascorbic acid low** - **E**xternal trauma — history evident - **D**rugs (anticoagulants) — history evident [cite:Park 26e Ch 8]