1 Department of Pediatric Endocrinology, VU University Medical Center, P.O. Box 7057, 1007 MB, Amsterdam, The Netherlands.
2 Department of Clinical Chemistry, VU University Medical Center, P.O. Box 7057, 1007 MB, Amsterdam, The Netherlands.
3 Department of Clinical Chemistry, VU University Medical Center, P.O. Box 7057, 1007 MB, Amsterdam, The Netherlands. Electronic address: [email protected].