The global medical process is a chain of different medical multidisciplinary procedures. The success in global Patient Safety will depend on the Safety of the consecutive medical processes that intervene in this complex system. Laboratory data is an essential part of health care, indeed it is used in 70% of clinical decisions. Inappropriate laboratory test over requesting is extremely frequent. The prevalence of under requesting has been less studied. The consequences of under requesting are clear, we are missing a diagnosis. Inappropriate over requesting can result not only in a problem of cost but also in a problem regarding patient safety. Additionally, another important consequence of inappropriate tests over requesting is that such amount of unnecessary tests has probably contributed to a significant increase in the volume of those over the last years. In all, there is general consensus that the inadequacy of test requesting must be corrected through strategies and monitored over time through indicators to assure the optimal laboratory contribution to clinical decision-making and patient safety.