One 7.5 mL serum separator tube (SST). Also acceptable: One 4 mL green top tube (heparin) or 4 mL plasma separator tube (PST).
Allow to clot, centrifuge and separate serum or plasma from cells and pour into plastic vial immediately. Refrigerate. Serum left in contact with cells for more than 3 hours may cause spurious results.
2 mL serum or plasma.
Avoid drawing from arm receiving intravenous transfusion. Patient should avoid exercising forearm before collection, which can cause an increase in potassium levels.
Gross hemolysis; freeze/thawing; serum on cells more than three hours.