Assessment of serum total 25-hydroxyvitamin D assays for Vitamin D External Quality Assessment Scheme (DEQAS) materials distributed at ambient and frozen conditions

Christopher T. Sempos, Emma L. Williams, Graham D. Carter, Julia C. Jones, Johanna E Camara, Carolyn Q Burdette, Grace Hahm, Federica Nalin, David L. Duewer, Adam J. Kuszak, Joyce Merkel, Andrew N. Hoofnagle, Pierre Lukas, Etienne Cavalier, Ramón Durazo-Arvizú, P.M. Crump, Christian Popp, Christian Beckert, Jan Schultess, Glen Van Slooten, Carole Tourneur, Camille Pease, Ravi Kaul, Alfredo Villarreal, Fiona Ivison, Ralf Fischer, Jody M.W. van den Ouweland, Chung Shun Ho, Emmett W. K. Law, Jean-Nicolas Simard, Renaud Gonthier, Brett Holmquist, Marcelo C. Batista, Sarah Meadows, Lorna Cox, Eugène Jansen, Dilshad Ahmed Khan, Kimberly Robyak, Michael H. Creer, Mark Kilbane, Patrick J. Twomey, James Freeman, Neil H. Parker, Jinyun Yuan, Robert L. Fitzgerald, Sohail Mushtaq, Michael W. Clarke, Norma Breen, Christine Simpson, Stephen A. Wise