1. Division of Endocrinology, Metabolism, and Molecular Medicine (H.A., N.F., A.D.), Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611
2. Departments of Laboratory Medicine and Pathology (S.K.G., R.J.S., R.L.T.), Mayo Clinic, Rochester, Minnesota 55905
3. Medicine (S.K.G.), Mayo Clinic, Rochester, Minnesota 55905