A 28-year-old male is brought to the mortuary with a history of drowning in a river 6 hours ago. The body shows frothy fluid in the mouth and nostrils, and the lungs appear waterlogged on external examination. Which investigation is most specific for confirming the diagnosis of drowning?

## Investigation of Choice in Drowning **Key Point:** Diatom analysis is the most specific confirmatory test for drowning because diatoms (siliceous algae) are present in water bodies and, if aspirated during drowning, are found in the lungs, bone marrow, and other organs. Their presence is pathognomonic for water aspiration. ### Why Diatom Analysis is Gold Standard **High-Yield:** Diatoms are: - Microscopic, siliceous-walled algae present in almost all natural water bodies - Aspirated into the lungs during the drowning process - Can penetrate into the pulmonary circulation and lodge in bone marrow, liver, and kidneys - Species-specific, allowing matching with water from the suspected drowning site - Resistant to decomposition, making them detectable even in advanced putrefaction ### Diagnostic Approach to Drowning | Investigation | Specificity | Utility | Limitations | | --- | --- | --- | --- | | **Diatom analysis** | Very high | Confirms water aspiration; species matching | Requires specialized microscopy; absent in some water bodies | | Histopathology | Moderate | Shows pulmonary edema, emphysema aquosum | Non-specific; seen in other asphyxial deaths | | Toxicology | Low | Rules out intoxication as contributing factor | Does not confirm drowning | | Chest radiology | Low | May show aspiration; post-mortem artifact common | Not confirmatory; poor specificity | ### Procedure for Diatom Analysis 1. Extract lung tissue and gastric contents 2. Digest organic matter with strong acid or alkali 3. Mount residue on glass slide 4. Examine under light microscopy (×400–1000 magnification) 5. Identify diatom species and compare with water sample from scene **Clinical Pearl:** The absence of diatoms does NOT rule out drowning (some water bodies are diatom-poor), but their presence is highly suggestive. Diatoms found in bone marrow are especially significant because they indicate ante-mortem aspiration and systemic circulation. **Warning:** ~~Frothy fluid in airways~~ alone is not diagnostic of drowning—it occurs in other asphyxial deaths and pulmonary edema from various causes. Histological pulmonary edema is common but non-specific. [cite:Reddy 34e Ch 8]