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 (preferred) or freeze. 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.