Objective: In vivo trombosis or bleeding, and in vitro fibrin formation occur in Multiple Myeloma (MM). We aimed to discuss the unavoidable in vitro fibrin formation in samples by reporting a MM case.

Case: A sixty-years-old man with a diagnosis of relaps MM whose specimens were rejected for insufficient sample. Also, some test results which incorrectly reported as possible erroneous were determined.

Discussion: In vitro fibrin formation in MM is sourced from abnormal fibrin formation in coagulation phase as a result of bleeding diathesis. Mechanisms of in vitro fibrin problem that commonly seen in preanalitic phase and disrupted the quality of samples in clinical laboratories, are agreed upon solution to improve the quality of laboratory results.