1. Department of Clinical Biology , Ziekenhuis Oost-Limburg , Genk , Belgium
2. Department of Laboratory Medicine , University Hospitals Leuven , Herestraat 49 , 3000 Leuven , Belgium , Phone: +32 16 34 70 34, Fax: +32 16 34 70 42
3. Department of Laboratory Medicine , University Hospitals Leuven , Leuven , Belgium
4. Department of Paediatric Endocrinology , University Hospitals Leuven , Leuven , Belgium