Serum samples: Collect blood from fasting subjects in a red top or yellow top serum collection tube. Immediately after blood collection, place the tubes upright in a rack and allow blood to clot at room temperature for 30 minutes to 2 hours. Centrifuge the tubes at 1500xg for 15 minutes and collect supernatant.   Plasma samples: Collect blood from fasting subjects in a tube containing either lithium heparin or EDTA (purple top). Invert tubes several times immediately after collection and place horizontally on a platform rocker at moderate speed for 30 minutes to 2 hours at room temperature. Centrifuge the tubes at 1500xg for 15 minutes and collect supernatant. Transfer 0.25 ml into a clean 0.5 to 2.0 ml cryogenic vial and store frozen until shipment. Smaller sample volumes can be accepted upon request, particularly for infant and pediatric studies.   Urine: collect first morning urine at mid-stream and transfer 0.25 ml into a clean 0.5 to 2.0 ml cryogenic vial and store frozen until shipment.