The Arsenic Blood (OS) Test (O.S. meaning Oral/Serum, but often for whole blood) is a blood test using ICP-MS to measure arsenic levels, primarily for detecting acute, recent arsenic poisoning from contaminated food/water/air, showing symptoms like nausea, abdominal pain, or neurological issues. Since arsenic leaves blood quickly (hours), it’s best for recent exposure (within days), with urine being better for longer-term monitoring, though blood tests confirm acute toxicity by detecting levels > 12 ng/mL, often requiring special metal-free tubes (like Royal Blue/EDTA)