© 2019 Biomedia. All rights reserved. With the growth and merging of clinical laboratories, very frequently analytical tests are performed on multiple instruments within one or multiple locations. In these situations, there is the need of verifying the comparability of patient results obtained with different analysers and/or different measurement procedures. The importance of this verification is further emphasised when considering that it is included into the ISO 15189 specifications. This protocol provides step-by-step guidance on how to assess results comparability in different scenarios. Up to four experimental designs are presented to meet laboratories' needs, with details and examples on frequency of testing, definition of acceptability criteria, samples selection, sample size calculation, statistical analysis and reporting.