3 mL whole blood in a royal blue trace metal-free tube with EDTA. Refrigerate. <br. Note: Diet, medication, and nutritional supplements may introduce interfering substances. Patients should be encouraged to avoid shellfish and seafood for 48-72 hours and discontinue nutritional supplements, vitamins, minerals, and non-essential over-the-counter medications (upon the advice of their physician) for 1 week prior to collection. Avoid exposure to contrast media for 96 hours prior to collection.