The study sample included all patients who had thiopurine metabolite analysis, complete blood count, and a comprehensive chemistry panel drawn within a 24 hour period at the University of Michigan between 1 May 2004 and 31 August 2006 and is described in greater detail in the manuscript.1 (link) This study was approved by the University of Michigan Medical Institutional Review Board with a waiver of explicit consent from the participants. The patient sample included 774 cases in a total of 346 individuals. For the analysis of the outcome of clinical response to thiopurines, 5 exclusion criteria were applied: exclusion of patients who did not have IBD, exclusion of patients who had not started on thiopurines at the time when the metabolites were measured, exclusion of patients on biological antitumour necrosis factor therapy, exclusion of patients without documentation of their clinical status at the time of laboratory measurement, and exclusion of patients who had an infection that confounded assessment of clinical response. This data set was used as the basis of a predictive model to identify patients with clinical response to thiopurine immune suppressant medication with a c statistic of 0.86.1 (link)