Prolonged Activated Partial Thromboplastin Time and False-Positive Results for Fibrinogen and Fibrin Degradation Products in a B-Cell Lymphoma Patient.

We report a unique case of a B-cell lymphoma patient in whom IgM monoclonal gammopathy resulted in a prolonged activated partial thromboplastin time (APTT) and false-positive results for fibrinogen and fibrin degradation products (FDPs). An 86-year-old man was referred to our hospital for further examination of abnormal cells in his peripheral blood. Laboratory data upon admission revealed an elevation of monoclonal IgM, presence of FDPs and marked prolongation of APTT (>180 s). Bone marrow examination revealed a predominant involvement of B lymphoma cells. In vitro examination revealed that IgM isolated from the patient's plasma had resulted in false-positive results for FDPs and APTT. Neither hemorrhagic nor thrombotic tendency was observed in this patient, suggesting that the abnormal coagulation data were due to interference by elevated monoclonal IgM levels.