SHORT COMMUNICATION Measurement uncertainty of 25-OH vitamin D determination with different commercially available kits: impact on the clinical cut offs E. Cavalier & E. Rozet & R. Gadisseur & A. Carlisi & M. Monge & J.-P. Chapelle & P. Hubert & J.-C. Souberbielle & P. Delanaye Received: 11 May 2009 / Accepted: 27 July 2009 / Published online: 9 September 2009 # International Osteoporosis Foundation and National Osteoporosis Foundation 2009 Abstract Summary Due to “measurement uncertainty”, the “true” 25-OH vitamin D (25(OH)D) of a patient (whatever the commercially available assay tested) will be >80 nmol/L if its measured concentration is >100 nmol/L. Thus, if a physician considers that a normal VTD status is a 25(OH)D level ≥80 nmol/L, he should ensure that the patient’ s results are ≥100 nmol/L. Introduction Many experts recommend that serum levels of 25(OH)D should be above a lower normal limit of 75– 80 nmol/L. However, the value delivered by laboratories is only an estimation of the “true” value due to “measurement uncertainty.” When using a cut off, measurement uncertainty around the cut off is important because therapeutic actions may differ if the measured value is below or above the limit. We aimed to establish the “measurement uncertainty” at different levels of concentration for several commercially available 25(OH)D analytical techniques. Methods We constituted three pools of serum with different 25(OH)D concentrations. Each pool was assayed in triplicate during 5 days with the DiaSorin RIA, Liaison, Elecsys, and Chromsystems-HPLC assays. Results We report a relatively high “measurement uncer- tainty” for the measurement of 25(OH)D for the four different techniques: the mean relative uncertainties, all techniques confounded were 19.4%, 16.0%, and 11.3% for pool 1 (35.3 nmol/L), pool 2 (79.5 nmol/L), and pool 3 (126.1 nmol/L), respectively. Conclusions Our results show that, whatever the assay, the “true” 25(OH)D of a patient will be >80 nmol/L if its measured concentration is >100 nmol/L. In other words, if a physician considers that a normal VTD status is defined by a 25(OH)D level ≥80 nmol/L, he should ensure that the patients present a 25(OH)D ≥100 nmol/L. Keywords 25-OH vitamin D . Hyperparathyroidism . Immunoassay . Measurement uncertainty . Target concentration Introduction Amongst other experts, Robert P. Heaney stated in 2000 in this Journal that the reference range of 25-OH vitamin D (25(OH)D) in serum should never be established according to a Gaussian distribution of an apparently “healthy” population [1]. On the other hand, there is no clear consensus on the limit value that could distinguish the E. Cavalier (*) : R. Gadisseur : A. Carlisi : J.-P. Chapelle Department of Clinical Chemistry, University Hospital of Liège, Domaine du Sart-Tilman, 4000 Liège, Belgium e-mail: Etienne.cavalier@chu.ulg.ac.be E. Rozet : P. Hubert Department of Analytical Chemistry, University of Liège, Liège, Belgium M. Monge Laboratoire Pasteur-Cerba, Saint Ouen L ’Aumône, Paris, France J.-C. Souberbielle Laboratoire d’Explorations Fonctionnelles, Hôpital Necker-Enfants Malades, Paris, France P. Delanaye Department of Nephrology, Dialysis and Hypertension, University Hospital of Liège, Liège, Belgium Osteoporos Int (2010) 21:1047–1051 DOI 10.1007/s00198-009-1052-5