Abnormal Fibrin Ultrastructure, Polymerization, and Clot Retraction in Multiple Myeloma*

We have investigated two patients with multiple myeloma who had a prolonged thrombin clotting time and absent clot retraction but no haemorrhagic diathesis. Coagulation and platelet function studies, as well as electron microscopy of the fibrin clot, indicate abnormal fibrin polymerization; adherence of myeloma protein to very thin fibrin strands results in a rigid translucent clot which fails to retract. This abnormality is not necessarily associated with a haemorrhagic diathesis.