The accuracy and reliability of laboratory tests play an important role in decision-making in the field of industry and services. These tests depend, in particular, on pre-analytical, analytical and post-analytical phases, and it is, therefore, unnecessary the related processes in detail and to know how to manage them. It is therefore recommended to comply with the requirements of ISO 17025:2017 and the use of risk management tools and procedures. The paper has a conceptual nature and summarizes the information from the literature, specifying the most common mistakes that occur in the various phases of testing.