A 2-year-old boy from rural Uttar Pradesh presents with bleeding gums, poor wound healing, and petechial rash over lower limbs. Dietary history reveals poor intake of citrus fruits and green leafy vegetables. Which investigation would best confirm the diagnosis of vitamin C deficiency?

Explanation

## Diagnosis of Vitamin C Deficiency (Scurvy) **Key Point:** Serum ascorbic acid level is the gold standard and most specific investigation for confirming vitamin C deficiency. Normal serum levels are > 0.6 mg/dL; deficiency is present when levels are < 0.2 mg/dL. ### Why Serum Ascorbic Acid? **High-Yield:** Serum ascorbic acid directly measures vitamin C status and is the most specific confirmatory test. It reflects recent dietary intake and is the standard biochemical marker for scurvy diagnosis. ### Investigations in Suspected Scurvy | Investigation | Finding in Scurvy | Role | |---|---|---| | **Serum ascorbic acid** | **< 0.2 mg/dL** | **Gold standard — most specific** | | Bleeding time | Normal (platelet function intact) | Supportive; helps rule out coagulation disorder | | PT/INR | Normal (vitamin K-dependent factors intact) | Supportive; rules out coagulopathy | | Platelet count | Normal or slightly elevated | Supportive; rules out thrombocytopenia | | Peripheral smear | May show "corkscrew" hairs (pathognomonic but rare) | Suggestive but not diagnostic | | Bone marrow | Hyperplastic (non-specific) | Not diagnostic; rarely needed | ### Pathophysiology of Bleeding in Scurvy ```mermaid flowchart TD A[Vitamin C Deficiency]:::outcome --> B[Impaired Collagen Synthesis] B --> C[Defective Blood Vessel Walls] C --> D[Capillary Fragility] D --> E[Bleeding & Petechiae]:::urgent A --> F[Impaired Wound Healing] A --> G[Bleeding Gums] B --> H[Defective Osteoid Formation] H --> I[Subperiosteal Hemorrhage] ``` **Clinical Pearl:** Bleeding in scurvy is due to defective collagen in blood vessel walls (not coagulation defect), so PT, PTT, and bleeding time are NORMAL. This is a key distinguishing feature from coagulation disorders. ### Clinical Features Supporting Scurvy Diagnosis **Mnemonic: SCURVY** - **S**wollen, bleeding gums - **C**orkscrew hairs (pathognomonic but rare) - **U**nhealed wounds - **R**ash (petechial, perifollicular) - **V**alue of citrus fruits (dietary history) - **Y**ellow teeth (discoloration) ### Diagnostic Approach 1. **Clinical suspicion** → Poor dietary intake of vitamin C, bleeding gums, petechiae, poor wound healing 2. **Serum ascorbic acid** → Confirmatory (< 0.2 mg/dL = deficiency) 3. **Coagulation studies** → Normal (rules out coagulopathy) 4. **Peripheral smear** → May show corkscrew hairs (supportive but rare) **Tip:** In NEET PG, when asked for the confirmatory test for scurvy, always choose serum ascorbic acid. Remember that coagulation parameters are normal in scurvy — this distinguishes it from bleeding disorders. [cite:Park 26e Ch 8, Harrison 21e Ch 95]