In forensic examination of a suspected snake bite victim, which of the following findings would help differentiate a dry bite from an envenomated bite?

Explanation

## Dry Bite vs. Envenomated Bite — Forensic Differentiation **Key Point:** The **20-minute whole blood clotting test (20-WBCT)** is the gold standard forensic marker for venom envenomation. A **positive 20-WBCT** (failure of blood to clot in 20 minutes) indicates systemic envenomation and coagulopathy. ### Diagnostic Features | Feature | Dry Bite | Envenomated Bite | |---|---|---| | **Fang marks** | May be present | Present | | **Local swelling** | Absent or minimal | Progressive, significant | | **Systemic symptoms** | Absent | Present (within 30 min–4 hrs) | | **20-WBCT** | **Normal (clots in ≤20 min)** | **Abnormal (no clot in 20 min)** | | **Coagulation profile** | Normal PT/INR, fibrinogen | Prolonged PT/INR, low fibrinogen | | **Platelet count** | Normal | Low (thrombocytopenia) | **High-Yield:** Dry bites account for **20–80%** of snake bites in India (depending on species and circumstances). The 20-WBCT is a **bedside, rapid test** that requires no equipment and is **highly sensitive for viper envenomation**. **Mnemonic:** **VIPER = Venom Induces Prolonged clotting in 20-minute test** — Remember that viper venom causes **consumption coagulopathy**, which is detected by 20-WBCT failure. **Clinical Pearl:** A **normal 20-WBCT at 20 minutes, 4 hours, and 24 hours post-bite** effectively rules out significant systemic envenomation and guides the decision to withhold antivenom. ### Why Other Options Don't Differentiate - **Fang marks alone** can be present in both dry and envenomated bites - **Absence of systemic symptoms within 4 hours** is suggestive but not definitive (some bites have delayed systemic effects) - **Local swelling confined to bitten limb** can occur in both dry and envenomated bites; envenomation typically causes **progressive, severe swelling** but this is subjective