THE JOURNAL OF VETERINARY EMERGENCY AND CRITICAL CARE • VOL, 9, NO. 2 • JUNE, 1999 • PAGE 79 Introduction The activated clotting time (ACT) is a simple yet rapid test utilized to assess the function of the intrinsic clotting cascade. It requires little technical expertise to perform the test or to in- terpret the results. The ACT utilizes diatoma- ceous earth as an inert activating agent to ini- tiate clotting through the intrinsic cascade. 1 Severe deficiency factors within either the in- trinsic or common cascade are likely to result in prolongation of the ACT. 2 Severe thrombocy- topenia, through lack of platelet factor 3, is also reported to potentially prolong the ACT. 1,2 The simplicity of the ACT makes it useful for assess- ing hemostatic dysfunction when no laboratory performed tests of hemostasis are available. Unfortunately, constant temperature heating blocks or waterbaths are not routinely found in general veterinary practice, limiting the ability of such practices to perform ACT. Previous stud- ies utilizing alternate sources of heat to per- Comparison of Axillary And Heating Block Methods of Activated Clotting Time (ACT) in Dogs Shane W. Bateman, DVM, DVSc Karol A. Mathews, DVM, DVSc The Department of Clinical Studies Ontario Veterinary College University of Guelph Guelph, ON, Canada N1G 2W1 Funding: Ontario Veterinary College Pet Trust Address reprint requests to: Dr. Shane W. Bateman Department of Veterinary Clinical Sciences The Ohio State University 601 Vernon L. Tharp Street Columbus, OH 43210-1089 Fax: 614-292-1454 Email: bateman.36@osu.edu Summary The activated clotting time (ACT) is commonly used in veterinary medicine as an assessment of dysfunction within the intrinsic clotting cascade. Performing the test requires little technical ex- pertise and no special equipment except for a heating block or constant temperature waterbath, neither of which is routinely found in veterinary practices. The purpose of this study was to determine whether performing the test using a human axilla as the heat source was accurate for both normal dogs and clinically ill dogs (with prolonged ACT’s), when compared to using a heat- ing block as the heat source. The results of this study reveal that the axillary method of ACT determination has acceptable clinical agreement with the heating block method. Thus, the axil- lary method of ACT determination is an acceptable alternative when no constant temperature heating source is available. Keywords activated clotting time, intrinsic clotting cascade, coagulation test, dogs