Thrombelastograph analyzers are point-of-care hemostatic analyzers that provide global assessment of the hemostatic process. Thrombelastography (TEG) detects and provides a continuous recording of the changes in the viscoelastic properties of whole blood from initial clot formation through fibinolysis. TEG has been validated for use in dogs, horses, and cats. Hemostasis research using TEG has focused on test validation, alterations of TEG tracings in animals with naturally occurring diseases, and the use of TEG for monitoring various therapeutic modalities. This article reviews TEG methodology and terminology, including potential sources of preanalytical and analytical errors, the correlation between TEG and other routine hemostatic assays, and current clinical applications of TEG, with emphasis on veterinary medical practice. Data suggest that TEG may be a sensitive and useful adjunctive tool for evaluating an animal with an underlying coagulopathy, including hypercoagulability and hypocoagulability. Additional prospective studies are needed to (1) correlate TEG tracing patterns with a clinical predisposition for bleeding or thrombosis in various disease states and (2) determine whether monitoring and treating hemostatic disorders based on TEG tracings improve clinical outcome.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1939-165X.2010.00263.x

Application of thrombelastography/thromboelastometry to veterinary medicine.

Objective

To systematically examine the evidence relating to the performance of rotational viscoelastic testing in companion animals, to develop assay guidelines, and to identify knowledge gaps.



Design

Multiple questions were considered within 5 parent domains, specifically system comparability, sample handling, assay activation and test protocol, definitions and data reporting, and nonstandard assays. Standardized, systematic evaluation of the literature was performed. Relevant articles were categorized according to level of evidence and assessed for quality. Consensus was developed regarding conclusions for application of concepts to clinical practice.



Setting

Academic and referral veterinary medical centers.



Results

Databases searched included Medline, Commonwealth Agricultural Bureaux abstracts, and Google Scholar. Worksheets were prepared evaluating 28 questions across the 5 domains and generating 84 assay guidelines.



Conclusions

Evidence-based guidelines for the performance of thromboelastography in companion animals were generated through this process. Some of these guidelines are well supported while others will benefit from additional evidence. Many knowledge gaps were identified and future work should be directed to address these gaps and to objectively evaluate the impact of these guidelines on assay comparability within and between centers.

Partnership on Rotational ViscoElastic Test Standardization (PROVETS): Evidence-based guidelines on rotational viscoelastic assays in veterinary medicine.

Immune-mediated hemolytic anemia (IMHA) causes severe anemia in dogs and is associated with considerable morbidity and mortality. Treatment with various immunosuppressive and antithrombotic drugs has been described anecdotally and in previous studies, but little consensus exists among veterinarians as to the optimal regimen to employ and maintain after diagnosis of the disease. To address this inconsistency and provide evidence-based guidelines for treatment of IMHA in dogs, we identified and extracted data from studies published in the veterinary literature. We developed a novel tool for evaluation of evidence quality, using it to assess study design, diagnostic criteria, explanation of treatment regimens, and validity of statistical methods. In combination with our clinical experience and comparable guidelines for humans afflicted with autoimmune hemolytic anemia, we used the conclusions of this process to make a set of clinical recommendations regarding treatment of IMHA in dogs, which we refined subsequently by conducting several iterations of Delphi review. Additionally, we considered emerging treatments for IMHA in dogs and highlighted areas deserving of future research. Comments were solicited from several professional bodies to maximize clinical applicability before the recommendations were submitted for publication. The resulting document is intended to provide clinical guidelines for management of IMHA in dogs. These guidelines should be implemented pragmatically, with consideration of animal, owner, and veterinary factors that may vary among cases.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/jvim.15463

ACVIM consensus statement on the treatment of immune-mediated hemolytic anemia in dogs.

Aortic thrombosis in dogs: presentation, therapy, and outcome in 26 cases.

Objective

To examine systematically the evidence on sample acquisition and handling for the thrombo elastography (TEG) and rotational thromboelastometry (ROTEM) viscoelastic point of care instruments and to identify knowledge gaps.



Design

Six questions were considered, addressing sampling site, collection system, anticoagulant, collection procedure, and sample storage. Standardized, systematic evaluation of the literature was performed. Relevant articles were categorized according to level of evidence (LOE). Consensus was developed regarding conclusions for application of concepts to clinical practice.



Setting

Academic and referral veterinary medical centers.



Results

PubMed and CAB abstracts were searched. Eighteen papers were initially chosen; 5 of these papers applied to > 1 domain question. Three papers were used to address 2 questions each, and 2 papers were used to address 3 questions each. Most papers were judged LOE 3 (Good or Fair). Two of 5 papers were judged to be the same LOE each time they were used; 2 papers were judged to be LOE 3, Fair for 1 question and 3, Good for a second question; 1 paper used to address 3 questions was judged LOE 3, Good twice and 3, Fair once. Fourteen additional papers were evaluated post hoc during manuscript preparation.



Conclusions

Jugular venipuncture is recommended, but samples from IV catheters can be used. Consistent technique is important for serial sampling, and standardized sampling protocols are recommended for individual centers performing TEG/ROTEM. There is insufficient evidence to recommend use of a specific blood collection system, although use of evacuated blood tubes and 21-Ga or larger needles is suggested. Use of 3.2% buffered sodium citrate in a strict 1:9 ratio of citrate to blood is suggested. Suggested tube draw order is discard/serum, followed by citrate, EDTA, and then heparin. Samples should be held at room temperature for 30 minutes prior to analysis.

Systematic evaluation of evidence on veterinary viscoelastic testing part 2: Sample acquisition and handling

Objective
To evaluate the effect of premedication on transfusion reactions (TRs) within 24 hours after blood product transfusions in dogs.

Design
Retrospective study between 2008 and 2011.

Setting
Private veterinary referral hospital.

Animals
Nine hundred and thirty-five transfusion events in 558 dogs.

Interventions
None.

Measurements and Main Results
Medical records of dogs receiving blood product transfusions were reviewed. Information collected included signalment, weight, transfusion product type, reason for transfusion, first or subsequent transfusion, whether an acute reaction occurred, type of reaction, whether the reaction was treated, premedication prior to the transfusion and the premedication used, other medications the animal was given, whether the animal had an immune-mediated process, and whether the transfusion was administered in the perioperative period. A total of 144 (15%) acute TRs were documented in 136 dogs. The most common TRs were fever alone (77/144 [53%]) and vomiting alone (26/144 [18%]). Six dogs died due to the TR (4%). TR was not associated with age (P = 0.257), sex (P = 0.754), weight (P = 0.829), or premedication (P = 0.312). The type of blood product transfused (P < 0.001) was significantly associated with TRs, with packed RBCs most likely associated with a TR, and plasma least likely. Immune disease (P = 0.015) was significantly associated with occurrence of a TR. Significantly fewer reactions were documented following transfusions given in the perioperative period (P = 0.023).

Conclusions
While most TRs were mild, there were some serious reactions observed including hemolysis, dyspnea, and 6 deaths. Immune-mediated disease was associated with development of a TR, while transfusion during the perioperative period was associated with lower likelihood of reaction. Packed RBC transfusions were associated with development of acute TRs. Overall occurrence of TR was not significantly altered with premedication; however, when evaluated alone, antihistamines decreased the incidence of acute allergic reactions.

Effect of premedication and other factors on the occurrence of acute transfusion reactions in dogs

Objective – To determine the effect of single and multiple doses of SQ heparin (200 U/kg) on the thrombelastogram of healthy dogs.



Design – Prospective study.



Setting – University research facility.



Animals – Six random-source female dogs.



Interventions – Baseline parameters, including a CBC with platelet count, prothrombin time, activated partial thromboplastin time (aPTT), and antithrombin were performed. Thrombelastography (TEG) and aPTT were performed hourly for 12 hours after unfractionated heparin dosing (200 U/kg, SQ). Anti-Xa activity was assayed at 0, 3, 6, and 8 hours. Heparin was then administered every 8 hours for 3 days. The sampling protocol on Day 4 was identical to Day 1.



Measurements and Main Results – On Day 1, percentage change from baseline for TEG parameter R, as well as absolute values of K, angle, and maximum amplitude (MA) were evaluated. Statistically significant (P<0.01) prolongation of the R time and a decrease in angle and MA was seen in all dogs by hour 3. R and MA were unmeasurable for most dogs between 3 and 5 hours. All TEG tracings returned to baseline by 12 hours. Day 4 TEG tracings mimicked those on Day 1. Only 1 dog achieved aPTT values outside the reference interval on both days. Anti-Xa activity levels increased on Day 4 but not on Day 1. Based on post hoc in vitro analysis, prolongation of R time occurred at plasma heparin levels as low as 0.075 U/mL, well below the lower limit of detection of the anti-Xa activity level assay.



Conclusions – Administration of SQ heparin results in progressive changes in the TEG tracing, with maximal change occurring 3–5 hours after dosing. The extensive prolongation of the R time also indicates that TEG may be too sensitive and limits its utility as a monitoring tool for unfractionated heparin therapy.

The effect of unfractionated heparin on thrombelastographic analysis in healthy 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.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1939-1676.2012.00907.x

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

Objective

To establish a standard protocol for analysis of canine whole blood and generate reference intervals for healthy dogs using the Sonoclot analyzer, and to compare Sonoclot values to standard and viscoelastic coagulation tests.



Design

Prospective study.



Setting

Veterinary University research facility and teaching hospital.



Animals

Twelve healthy random source dogs and 52 healthy dogs from the general veterinary school population. Interventions: Blood sampling for viscoelastic coagulation testing.



Measurements and Main Results

Blood was collected from 12 healthy adult dogs by jugular venipuncture. After a rest period at room temperature of 30, 60, or 120 minutes, 340 μL of citrated blood was added to 20 μL of 0.2 M CaCl2 in 1 of 2 cuvette types warmed to 37° C. Cuvettes contained a magnetic stir-bar with glass beads (gbACT+) or only a magnetic stir-bar (nonACT). Reference interval samples were collected from 52 healthy adult dogs and analyzed in duplicate. The ACT, CR, and PF were not affected by duration of rest period for either cuvette type. ACT variability was decreased when using gbACT+ cuvettes (P < 0.05). In normal dogs reference intervals (mean ± 2 SD) using gbACT+ cuvettes were: ACT 56.0–154.0 seconds, CR 14.85–46.0, and PF 2.1–4.05. ACT correlated to TEG R-time, K-time, and angle, while CR correlated with all TEG parameters. Fibrinogen correlated with ACT, CR, and PF. Sonoclot did not correlate with other common coagulation tests.



Conclusions

Sonoclot provides viscoelastic evaluation of canine whole blood coagulation and correlated to several TEG parameters and fibrinogen. A standard protocol and reference intervals were established.

Sonoclot evaluation of whole blood coagulation in healthy adult dogs.

Objective

To determine the effects of rest temperature, contact activation (CA), and sample collection technique on thrombelastography (TEG) using canine whole blood.



Design

Prospective, experimental study.



Setting

University-based research facility.



Animals

Twelve healthy, adult, mixed-breed dogs.



Interventions

Blood was collected by jugular venipuncture. Tubes containing 3.2% sodium citrate, with and without 75 μg/mL corn trypsin inhibitor (CTI), were filled by vacuum. Samples rested for 30 minutes at 3 temperatures: 37°C, room temperature (RT, 20–22°C), or warmed to 37°C 5 minutes prior to analysis (prewarmed). Samples were analyzed at 37°C. CTI-treated samples were analyzed with and without 1:50,000 tissue factor (TF) as activator. Six dogs were also tested similarly using a needle/syringe collection technique.



Measurement and Main Results

Prewarmed samples exhibited greater MA compared to RT (55.5 ± 7.2 mm vs. 53.5 ± 6.0, P< 0.05), while 37°C samples exhibited a steeper angle (56.7 ± 10.4°C vs. 52.4 ± 8.6°C) and greater MA (55.9 ± 7.5 mm vs. 53.5 ± 6.0 mm) than RT samples (both P< 0.05). CTI-treated samples were hypocoagulable (R time 45 min [7.5–56.8 min], angle 8.2°C [5.1–42.5°C], MA 29.2 ± 9.7 mm, P< 0.001), with TF activation returning all but the angle (42.5 ± 7.6°C) to values similar to citrated samples (angle = 56.7 ± 10.4°C, P = 0.017). Collection using a syringe/needle method revealed a shorter R time for prewarmed samples only (R time 4.7 ± 0.7 min, vs. 5.6 ± 0.8 min for vacuum-collected samples, P = 0.008).



Conclusions

Even in the absence of exogenous activators, CA has an impact on canine TEG results. The effects of rest temperatures and sample collection technique on TEG appear to be minimal.

Jennifer R. Pittman

Papers

Effect of premedication and other factors on the occurrence of acute transfusion reactions in dogs

The effect of unfractionated heparin on thrombelastographic analysis in healthy dogs.

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

Sonoclot evaluation of whole blood coagulation in healthy adult dogs.

Effects of rest temperature, contact activation, and sample technique on canine thrombelastography