Royal blue (trace element) and/or Metal-Free aliquot tubes are available from MLabs (800-862-7284). Collect blood in a royal blue top (trace element) tube with no preservative (serum). Allow specimen to clot for 30 minutes, centrifuge, and carefully pour serum into a metal-free aliquot tube, avoiding transfer of the cellular components of blood. Do not insert a pipet into the serum to transfer and do not ream the specimen with a wooden stick to assist with the transfer. Refrigerate up to 48 hours or freeze for longer storage. Do not collect specimens for trace metal testing from patients who have received gadolinium-, iodine-, or barium-containing contrast material within the past 96 hours. These metal-based contrast agents are known to interfere with laboratory techniques commonly used for trace metals analysis.