In the clinical laboratory to allow an effective testing process, post-analytical activity can have two goals in trying to improve patient safety: result interpretation and communication of critical values. Both are important issues, and their success requires a cooperative effort. Misinterpretation of laboratory test results or ineffectiveness in their notification can lead to diagnostic errors or errors in identifying patient critical conditions. With the awareness that the incorrect interpretation of tests and the breakdown in the communication of critical values are preventable errors, laboratorians should make every effort to prevent the types of errors that potentially harm patients. In order to improve the reliability of laboratories, we attempt to explain how interpretative reporting and automated notification of critical values can be used to reduce errors. Clinical laboratories can therefore work to improve clinical effectiveness, without forgetting that everything should be designed to provide the best outcomes for patients.