• Open Access

Treatment of Immune-Mediated Hemolytic Anemia with Individually Adjusted Heparin Dosing in Dogs


  • Dr Finke is presently affiliated with Wheat Ridge Animal Hospital, Wheat Ridge, CO. Dr Helmond is presently affiliated with Cornell University College of Veterinary Medicine, Ithaca, NY. Presented in part at the 27th Annual American College of Veterinary Internal Medicine (ACVIM) forum, Montreal, Canada, 2009. The study was performed at the University of Minnesota Veterinary Medical Center, Saint Paul, Minnesota MN.

Corresponding author: Dr David Polzin, Department of Veterinary Clinical Sciences, University of Minnesota, 1365 Gortner Avenue, Saint Paul, MN 55108-6192; email: polzi001@umn.edu.


Background: A major cause of death in dogs with immune-mediated hemolytic anemia (IMHA) is thromboembolism. Previous studies suggest unfractionated heparin (UH) is not effective in preventing thromboembolism in IMHA; however, subtherapeutic dosing could explain the seeming lack of efficacy.

Hypothesis: Providing therapeutic plasma concentration of UH by individually adjusting doses based on antifactor Xa activity would improve survival in IMHA.

Animals: Fifteen dogs with primary IMHA.

Methods: Randomized, prospective, controlled clinical trial. Dogs received standardized therapy for IMHA and either constant dose (CD) (150 U/kg SC) (n = 7) or individually adjusted dose (IAD) (n = 8) UH, monitored via an anti-Xa chromogenic assay, adjusted according to a nomogram. UH was administered every 6 hours until day 7, and every 8 hours thereafter. UH dose was adjusted daily in IAD dogs until day 7, weekly until day 28, then tapered over 1 week. Dogs were monitored for 180 days.

Results: At day 180, 7 dogs in the IAD group and 1 in the CD group were alive (P= .01). Median survival time for the IAD group was >180 days, and 68 days for the CD group. Thromboembolic events occurred in 5 dogs in the CD group and 2 dogs in the IAD group. Doses of UH between 150 and 566 U/kg achieved therapeutic anti-Xa activity (0.35–0.7 U/mL).

Conclusions and Clinical Importance: This study suggests that IAD UH therapy using anti-Xa monitoring reduced case fatality rate in dogs with IMHA when compared with dogs receiving fixed low dose UH therapy.