1. Department of Clinical Chemistry , VU University Medical Center , Amsterdam , The Netherlands
2. Department of Pediatric Endocrinology, VU University Medical Center , Amsterdam , The Netherlands
3. Department of Laboratory Medicine, Radboud University Medical Center, Geert Grooteplein 10 , 6525 GA Nijmegen , The Netherlands
4. Department of Biochemistry , Stellenbosch University , Stellenbosch , South Africa