[Increased thrombin time in a patient with multiple myeloma].

We describe a 56-year-old patient with multiple myeloma and very high paraprotein concentration (IgG kappa). Coagulation studies showed unclottable thrombin and reptilase times caused by impaired fibrin polymerization presumably due to the paraproteinemia. There was no obvious bleeding tendency. The differential diagnosis of thrombin time prolongation includes inhibition of the added thrombin by exogenous heparin, hirudin or seldom by endogenous heparin-like anticoagulants or by acquired (bovine) thrombin antibodies, qualitative fibrinogen disorders (congenital and acquired dysfibrinogenemia), quantitative fibrinogen disorders (severe hypo- and afibrinogenemia) and delayed fibrin polymerization due to fibrin/fibrinogen degradation products, paraproteins and antibodies against fibrin(ogen). In multiple myeloma, thrombin time prolongation may seldom be due to endogenous heparin-like anticoagulants or antibodies to thrombin and more frequently to impaired fibrin polymerization by paraproteins. Simultaneous reptilase time prolongation as present in this case hints to this latter possibility.