The diagnostic workup of veterinary patients is a decision-making process. For the decision-making processes to be consistent, established decision criteria are essential. These criteria may be in the form of decision limits or population-based and subject-based reference intervals (RIs). One solution to the frequent problem of small reference sample sizes is to harvest results from laboratory databases, a procedure called data mining. The suitability of a particular population for RI generation assumes homogeneity in that population. Unlike RIs that are descriptive of the distribution of blood values in healthy subjects, a decision limit is a predetermined test threshold that distinguishes between two subgroups of a target population. Reference intervals typically are printed on laboratory reports along with patient results. This only should be done when the provided RIs are applicable to the patient demographic.