In vitro hypercoagulability on whole blood thromboelastometry associated with in vivo reduction of circulating red cell mass in dogs

Background: Previous studies have reported a strong correlation between indicators of red cell mass (RCM) and thromboelastometry results (TEM) in several species, specifically an association of apparent hypercoagulability with decreased RCM. Objectives: The objectives of the study were to (1) evaluate the effect of decreased circulating RCM on TEM results in dogs, and (2) determine the relative contributions of citrate dilution vs in vivo reduction of RCM to hemostatic potential. Materials and Methods: Thirteen healthy dogs had one unit of blood removed on day 0. Whole blood, EDTA, and citrated blood samples for evaluation of TEM variables and PT, APTT, platelet count, fibrinogen, thrombin-antithrombin (TAT), and thrombin generation were collected at baseline, and 3 and 21 days after blood removal. Blood samples were also corrected to a PCV of 45% by adding citrate or removing plasma. Results: On day 3 after blood removal, the PCV was significantly decreased (45 ± 6%) compared with baseline (52 ± 6%) and day 21 (50 ± 4%, P < .001), accompanied by TEM variables indicating hypercoagulability, which returned to baseline values by day 21. Other coagulation variables such as PT, APTT, platelet count, TAT, or plasma thrombin generation remained unchanged, with the exception of fibrinogen that was significantly higher on day 3. No changes were related to citrate dilution. Conclusions: Transiently decreased RCM in vivo was accompanied by TEM variables indicating hypercoagulability, which was not confirmed by other coagulation variables. This suggests an artifact of TEM, which presents a potential limitation of this technology in patient populations with abnormal RCM.