Eat an evening meal containing 250g MARINE fish eg shark NOT TUNA. Fish and chips is good but ensure the fish component is actual fish (not batter). Alternatively 2 eggs and 400g "baked" haricot or soya beans, or 250g liver or kidney. Collect first urine next morning.
If overnight - Frozen
LCMS we measure both Trimethylamine and Trimethylamine oxide and report TMA to total amine ratio