Anti-heparin activity of a macroglobulin from a patient with breast adenocarcinoma

We describe a case of IgM paraproteinemia, whose macroblogulin reacted anomalously with heparin. Anti-heparin activity of the paraprotein was suggested by insensibility of the patient's plasma to heparin in heparin-thrombin clotting time. Moreover, the presence of heparin in the medium markedly reduced the inhibitory effect of the paraprotein on platelet aggregation by ADP.