A 32-year-old woman from rural Maharashtra presents to the emergency department with acute onset of severe abdominal pain, profuse watery diarrhea, and vomiting for 6 hours. Her husband reports she consumed food prepared by a neighbour. On examination, she is hypotensive and has signs of severe dehydration. Serum electrolytes show hypokalaemia and hyponatraemia. Clinical suspicion of acute arsenic poisoning is high. Which investigation is most appropriate for confirming arsenic poisoning?

Explanation

## Investigation of Choice in Acute Arsenic Poisoning **Key Point:** In acute arsenic poisoning, 24-hour urine arsenic level is the gold standard confirmatory investigation because arsenic is rapidly excreted in urine within 24–72 hours of ingestion. ### Rationale for Correct Answer 24-hour urine arsenic measurement is preferred in acute poisoning because: 1. Arsenic is rapidly absorbed and excreted renally (>80% within 48 hours) 2. Urine levels are significantly elevated in acute poisoning (normal: <50 μg/L; acute: >1000 μg/L) 3. Timing is critical — urine must be collected within 24–48 hours of ingestion for maximum yield 4. Non-invasive and easily repeatable ### Comparison of Arsenic Detection Methods | Investigation | Timing | Sensitivity in Acute Poisoning | Clinical Use | |---|---|---|---| | **24-hour urine arsenic** | Within 24–72 hrs of ingestion | Very high (>1000 μg/L) | **Gold standard for acute poisoning** | | Serum arsenic | Immediate (first few hours) | Moderate; rapidly falls | Less reliable; short window | | Hair arsenic | Weeks to months after exposure | High for chronic exposure | Chronic poisoning / forensic cases | | Nail arsenic | 3–6 months after exposure | High for chronic exposure | Historical exposure; Mees' lines | **High-Yield:** Urine arsenic >50 μg/L is abnormal; >1000 μg/L is diagnostic of acute poisoning. Serum levels fall rapidly and are unreliable after 24 hours. ### Clinical Pearl In this acute presentation with gastrointestinal symptoms and electrolyte derangement, the 24-hour urine collection should be initiated immediately upon hospital admission to capture peak excretion. Supportive care (IV fluids, electrolyte correction, activated charcoal if within 4 hours) should not be delayed pending investigation results. ### Why Hair and Nail Analysis Are Not First-Line Here Hair and nail arsenic accumulate over weeks to months and reflect chronic or subacute exposure. They are valuable in forensic medicine for documenting historical poisoning (e.g., exhumation cases, suspected repeated dosing) but are not sensitive for acute poisoning where urine is the target matrix.