1. Department of Endocrinology and University of Groningen, Groningen, The Netherlands.
2. Department of Nuclear Medicine and Molecular Imaging; University of Groningen, Groningen, The Netherlands.
3. Department of Clinical Chemistry and Hematology, Laboratory of Endocrinology, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands.
4. Department of Clinical Chemistry, Endocrine Laboratory, VU University Medical Center, VU University, Amsterdam, The Netherlands.
5. Department of Laboratory Medicine; University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.