A 3-year-old child from rural India presents with bleeding gums, petechiae, and a prothrombin time (PT) of 18 seconds (normal 12–14 s). Vitamin K-dependent coagulation factors are low. Which feature would best distinguish vitamin K deficiency from vitamin D deficiency in this child?

Question

Accepted Answer

D. Prolonged PT/INR with normal bleeding time and normal platelet count. ## Distinguishing Vitamin K from Vitamin D Deficiency

### Clinical and Laboratory Comparison

| Feature | Vitamin K Deficiency | Vitamin D Deficiency |
|---------|----------------------|----------------------|
| **Bleeding manifestations** | Petechiae, ecchymosis, GI bleed, gum bleeding | No bleeding |
| **PT/INR** | **Prolonged** (↑ PT) | Normal |
| **Bleeding time** | **Normal** | Normal |
| **Platelet count** | **Normal** | Normal |
| **Calcium** | Normal | **Low** (hypocalcemia) |
| **Alkaline phosphatase** | Normal | **Elevated** |
| **Bone findings** | Normal | Rickets (metaphyseal lucencies, widening) |
| **Muscle** | Normal strength | Weakness, myopathy |

### Mechanism of Coagulopathy in Vitamin K Deficiency

**Key Point:** Vitamin K is an essential cofactor for γ-carboxylation of prothrombin (Factor II), Factors VII, IX, and X. Without it, these **vitamin K-dependent factors** cannot be synthesized in functional form, leading to prolonged PT/INR.

**High-Yield:** The **PT is prolonged because Factors II, VII, and X are vitamin K-dependent**. The **bleeding time remains normal** because platelet function and fibrinogen are unaffected. This pattern is pathognomonic for vitamin K deficiency.

**Clinical Pearl:** In vitamin D deficiency, the bleeding time and PT are both normal because coagulation is not affected. The clinical picture is dominated by **hypocalcemia** (tetany, seizures) and **rickets** (bone deformity, metaphyseal lucencies).

### Why Option 0 Is the Best Discriminator

**Mnemonic: "K for Koagulation, D for Deposition (of calcium)"**
- **K** → **K**oagulation defect (prolonged PT, normal bleeding time)
- **D** → **D**eposition defect (hypocalcemia, rickets)

Prolonged PT with normal bleeding time and normal platelet count is:
1. **Specific to vitamin K deficiency** (no other common deficiency causes this pattern)
2. **Absent in vitamin D deficiency** (PT is normal in D deficiency)
3. **Clinically testable** and immediately actionable (vitamin K replacement reverses the PT within hours to days)

Answer

A. Muscle weakness with elevated creatine kinase and normal prothrombin time

Answer

B. Elevated liver enzymes with jaundice and steatorrhea

Answer

C. Hypocalcemia with elevated alkaline phosphatase and metaphyseal lucencies on X-ray

A 3-year-old child from rural India presents with bleeding gums, petechiae, and a prothrombin time (PT) of 18 seconds (normal 12–14 s). Vitamin K-dependent coagulation factors are low. Which feature would best distinguish vitamin K deficiency from vitamin D deficiency in this child?

Explanation

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