How Accurate Are Assays for 25-Hydroxyvitamin D? Data from the International Vitamin D External Quality

Data from the International Vitamin D External Quality Assessment Scheme, Graham D. Carter, Richard Carter, Julia Jones, and Jacqueline Berry ( Endocrine Laboratory, Clinical Chemistry Department, Charing Cross Hospital, London, United Kingdom; 2 Sovereign Software Services, Haywards Heath, West Sussex, United Kingdom; 3 Vitamin D Research Group, Medicine, Manchester Royal Infirmary, Manchester, United Kingdom.: * address correspondence to this author at: Endocrine Laboratory, Clinical Chemistry Department, Charing Cross Hospital, Fulham Palace Road, London, W6 8RF, United Kingdom; fax 44-208-846-7007, e-mail julia.jones@imperial.ac.uk)