1. From the Department of Endocrinology/Diabetes Center (M.D.), VU University Medical Center, Amsterdam, the Netherlands; the Departments of Endocrinology (M.D., J.W.A.S., J.K.R.) and Clinical Chemistry (R.N., R.F.P., A.S.), Leiden University Medical Center, Leiden, the Netherlands; and the Department of Clinical Chemistry (R.N., A.S.), Academic Medical Center, Amsterdam, the Netherlands.