A 35-year-old man is found dead in a burnt house. The body shows extensive charring with a pugilistic attitude. On autopsy, the lungs appear bright pink and frothy fluid is present in the airways. Which investigation is most appropriate to confirm ante-mortem burning?

## Investigation of Choice for Confirming Ante-mortem Burns ### Key Diagnostic Principle **Key Point:** Carboxyhemoglobin (COHb) estimation is the gold standard investigation to differentiate ante-mortem from post-mortem burns because it directly proves the victim was breathing and alive during the fire. ### Why COHb Estimation is Diagnostic **High-Yield:** In ante-mortem burns, the victim inhales toxic gases (carbon monoxide, smoke) while breathing. Carbon monoxide binds to hemoglobin with an affinity ~200 times greater than oxygen, forming carboxyhemoglobin. Blood COHb levels >10–15% in a burn victim indicate ante-mortem exposure. **Clinical Pearl:** The bright pink discoloration of lungs and frothy fluid in the airways (seen in this case) are suggestive of ante-mortem burning, but these are circumstantial findings. Only COHb estimation provides biochemical proof of inhalation during life. ### Comparison of Investigations | Investigation | Ante-mortem Burns | Post-mortem Burns | Specificity | |---|---|---|---| | **COHb estimation** | >10–15% (diagnostic) | Absent or <3% | **Highest** | | Soot in airways | Present | May be present (passive) | Low | | Skin histology (heat changes) | Present | Present | Cannot differentiate | | Body temperature | Variable | Not useful | None | ### Mechanism 1. Victim inhales smoke and CO during fire → CO enters lungs 2. CO diffuses across alveolar membrane → binds to hemoglobin 3. Forms stable carboxyhemoglobin (COHb) 4. Post-mortem: no inhalation → no COHb formation **Key Point:** A COHb level >10% is considered evidence of ante-mortem inhalation. Levels >50% indicate death from CO poisoning before significant thermal injury. ### Limitations of Other Findings - **Bright pink lungs & frothy fluid:** Suggestive but not diagnostic (can occur post-mortem from heat-induced fluid release) - **Soot in airways:** Can be passively deposited post-mortem - **Pugilistic attitude:** Heat-induced muscle contraction, occurs post-mortem [cite:Reddy Forensic Medicine 33e Ch 8]