We present a case of analytical interference on three parameters (lactate dehydrogenase, uric acid and alkalin phosphatase), caused by a monoclonal IgM, evidenced in a patient with Waldenström disease. Mechanism of interference was probably related to the formation of complexes between paraprotein and lithium heparin, which result in precipitation during clinical chemistry assays, inducing a bias in the results. Management recommendations in case of suspicion of interference in clinical chemistry analysis are detailed. Are discussed for the case report, clinical consequences, possible mechanisms and evolution of interference under treatment, according to the concentration of the monoclonal protein.