A prospective study of unfractionated heparin therapy in dogs with primary immune-mediated hemolytic anemia.

Unfractionated heparin therapy was initiated at a standard dosage of 300 IU/kg subcutaneously q 6 hours to 18 dogs with immune-mediated hemolytic anemia. Heparin's prolongation of activated partial thromboplastin time and change in factor Xa inhibition (anti-Xa activity) were serially monitored during the first 40 hours of therapy. During the initial 40 hours, only eight of 18 dogs had attained anti-Xa activities of > or =0.35 U/mL. No dogs had clinical signs of hemorrhage. Fifteen dogs survived to discharge; 11 dogs were alive at 1 year, and thrombosis was identified in three of six nonsurvivors that were necropsied.