Medical laboratories and their reports significantly impact the decisions made by clinicians. Interference for different reasons can threaten the reliability of these results. Many studies have investigated the causes and effects of interferences. This review describes the causes of interferences encountered in various biochemical, haematological and urinalysis tests frequently measured in clinical laboratory practice and the methods to deal with them. To obtain accurate results, laboratory specialists must be aware of interferences, know handling strategies with them, and contact the clinician when necessary.