• Open Access

Sonoclot® Evaluation of Single- and Multiple-Dose Subcutaneous Unfractionated Heparin Therapy in Healthy Adult Dogs


  • This work was performed at the College of Veterinary Medicine, Athens, GA.
  • Portions of this work have been presented in abstract form at the International Veterinary Emergency and Critical Care Symposium 2010 (San Antonio, TX).

Corresponding author: B.M. Brainard, VMD, Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, 501 D.W. Brooks Dr, Athens, GA 30602; e-mail: brainard@uga.edu.



Heparin therapy is difficult to monitor due to variation in animal response. While laboratory measurements of activated partial thromboplasin time (aPTT) and Anti-Xa activity (AXA) accurately describe heparin effect, their availability is limited.


Sonoclot analysis would be as sensitive as AXA and aPTT to monitor effects of unfractionated heparin (UFH) in healthy adult dogs.


Six adult mixed-breed dogs.


A prospective study design was employed. On day 1, baseline samples were collected (CBC, PT, aPTT, and Sonoclot), and UFH (300 U/kg SC) was administered to 6 dogs following an IV loading dose of 50 U/kg. Sonoclot and aPTT were performed hourly for 12 hours. AXA was assayed at hours 3, 6, 9, and 12. UFH (300 U/kg q8 h SC) was administered at 12 hours, and subsequently (q8 h) for 2 additional days. On day 4, a final dose of UFH was administered, and a sampling protocol identical to day 1 was performed.


Sonoclot activated clotting time (ACT) and clot rate (CR) correlated with AXA (R = 0.69, R = 0.65, respectively, P < .001), although to a lesser degree than aPTT (R = 0.75, P < .001). Linear regression using ACT and CR as covariates indicated a stronger correlation with AXA (R = 0.73, P < .001). ACT values strongly correlated with aPTT (R = 0.87, P < .001).

Conclusions and Clinical Importance

Administration of UFH to healthy dogs results in progressive changes in Sonoclot values. AXA was correlated with a combination of ACT and CR and with aPTT. Sonoclot may play a role in monitoring UFH therapy; however, prospective studies evaluating its utility in clinical cases are warranted.