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

Background 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. Hypothesis Sonoclot analysis would be as sensitive as AXA and aPTT to monitor effects of unfractionated heparin (UFH) in healthy adult dogs. Animals Six adult mixed‐breed dogs. Methods 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. Results 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.