By Carl A. Burtis, PhD, Health Services Division, Oak Ridge National Laboratory, Oak Ridge, TN, and Clinical Professor of Pathology, University of Utah School of Medicine, Salt Lake City, UT and David E. Bruns, MD, Professor of Pathology, University of Virginia School of Medicine, Director of Clinical Chemistry and Associate Director of Molecular Diagnostics, University of Virginia Health System, Charlottesville, VA, and Former Editor, Clinical Chemistry, Washington, DC