Clinical pathology data are routinely collected during animal health studies in order to aid in the evaluation of a compound’s toxicity profile. Clinical pathology test results can be affected by factors occurring prior to sample analysis (preanalytical) and it is the potential impact of these factors, in particular, which can be easily overlooked at the time of data interpretation. Anne Provencher, Executive Director of Clinical Pathology for Global Preclinical Services, and William Siska, Clinical Pathologist, at Charles River, discuss the need for in-depth consideration of preanalytical variables, during both study design and study conduct, in order to reduce their potential impact on clinical pathology data.