A 38-year-old man presents to the emergency department with acute onset of severe abdominal pain, profuse watery diarrhea, and vomiting for 6 hours. He reports exposure to pesticide-contaminated food at a local restaurant. On examination, he is hypotensive and dehydrated. Clinical suspicion for acute arsenic poisoning is high. Which investigation is most appropriate for confirming arsenic toxicity?

Explanation

## Investigation of Choice for Acute Arsenic Poisoning **Key Point:** In acute arsenic poisoning, 24-hour urinary arsenic level is the gold standard investigation for confirmation and assessment of toxicity severity. ### Why 24-Hour Urinary Arsenic? 1. **Timing of excretion**: Arsenic is rapidly absorbed and excreted primarily through the kidneys within 24–72 hours of acute exposure. 2. **Quantification**: Provides accurate quantitative measurement of absorbed arsenic burden. 3. **Clinical correlation**: Levels >50 μg/L in 24-hour urine are diagnostic of acute poisoning. 4. **Prognostic value**: Higher urinary levels correlate with severity of poisoning and organ involvement. **High-Yield:** In acute poisoning, collect urine within 24–48 hours of exposure for maximum diagnostic yield. Levels should be measured using atomic absorption spectrophotometry (AAS) or inductively coupled plasma mass spectrometry (ICP-MS). ### Comparison of Arsenic Detection Methods | Investigation | Timing | Use Case | Sensitivity | |---|---|---|---| | **24-hour urinary arsenic** | Acute (24–72 hrs) | Acute poisoning confirmation | Highest in acute phase | | Serum arsenic | Acute (first 24 hrs) | Very early detection only | Low; rapidly cleared | | Hair/nail arsenic | Chronic (weeks–months) | Chronic exposure assessment | Best for remote/chronic exposure | | Fecal arsenic | Variable | Non-invasive but unreliable | Poor correlation with toxicity | **Clinical Pearl:** Baseline normal urinary arsenic is <10 μg/L. Acute poisoning typically shows >50 μg/L; chronic exposure may show 10–50 μg/L. ### Specimen Collection Guidelines - Collect 24-hour urine in acid-washed, arsenic-free containers. - Refrigerate specimen during collection. - Send promptly to toxicology laboratory. - Avoid contamination from environmental sources. **Mnemonic:** **URINE24** = Urinary Investigation for Rapid INtoxication Evaluation (24-hour collection)