Evaluation of platelet function screening tests to detect platelet procoagulant deficiency in dogs with Scott syndrome

A prospective cohort study to identify clinical diagnostic and prognostic markers of primary immune thrombocytopenia in dogs

BACKGROUND

Primary immune thrombocytopenia (pITP) in dogs presents a diagnostic challenge, and clinical markers of severity are lacking.

OBJECTIVES

Identify clinicopathologic features that differentiate pITP from secondary ITP (sITP) and markers related to bleeding severity, transfusion, and survival of dogs with pITP.

ANIMALS

Ninety-eight thrombocytopenic dogs (58 pITP and 40 sITP).

METHODS

Client-owned dogs with platelet counts <50 000/μL were enrolled in a prospective, multi-institution cohort study. History and treatment information, through a maximum of 7 days, was recorded on standard data forms. Bleeding severity was scored daily using a bleeding assessment tool (DOGiBAT). At-admission blood samples were collected for CBC, biochemistry, C-reactive protein concentration, and coagulation panels, and to measure platelet surface-associated immunoglobulin G (PSAIg) and expression of platelet membrane proteins and phospholipids. Dogs with evidence of coincident disease were classified as sITP.

RESULTS

No definitive pITP diagnostic test was found. However, pITP cases were characterized by lower platelet counts, D dimer concentrations, and platelet membrane protein expression than sITP cases. Differentiation between pITP and sITP was further enhanced using logistic regression modeling combining patient sex, coagulation profile, platelet count, D dimer, and PSAIg. A second model of pITP severity indicated that low hematocrit and high BUN concentration were associated with non-survival. Low hematocrit at admission, but not platelet count or DOGiBAT score, was associated with transfusion.

CONCLUSIONS AND CLINICAL IMPORTANCE

Pending validation studies, models constructed from at-admission clinicopathologic findings may improve differentiation of pITP from sITP and identify the most severe pITP cases at the time of presentation.

Point-of-care platelet function testing results in a dog with Bernard-Soulier syndrome

Bernard-Soulier syndrome (BSS), also known as hemorrhagiparous thrombocytic dystrophy (OMIA 002207-9615), is a rare defect in platelet function recognized in both dogs and humans. It is caused by a deficiency in glycoprotein 1b-IX-V, the platelet surface protein which acts as a receptor for the von Willebrand factor. The characteristic features of BSS in humans and dogs include macrothrombocytes and mild-to-moderate thrombocytopenia with a bleeding tendency. This condition has previously been reported in European Cocker Spaniel dogs; however, the results of platelet function tests in these animals have not been reported. This case report describes a European Cocker Spaniel dog with spontaneously occurring Bernard-Soulier syndrome and the results of point-of-care platelet function tests, including a prolonged buccal mucosal bleeding time (>8 min), prolongation (>300 s) of PFA-200 COL/ADP, COL/EPI, and P2Y closure times, and reduced aggregation (15%-48%) with Plateletworks ADP, but with normal aggregation (92%) with Plateletworks AA. This is the first description of the results of platelet function tests in canine Bernard-Soulier syndrome.

Clinical Assessment of Primary Hemostasis: A Review

Primary hemostatic disorders such as thrombocytopenia and thrombocytopathia are commonly encountered in small animal practice. The key stages of primary hemostasis include platelet adhesion, activation, and aggregation. Understanding the interaction between tissues, platelets, and signaling molecules not only helps clinicians comprehend clot formation but also better recognize thrombocytopathias. Although congenital thrombocytopathia is rare, commercially available platelet function tests allow veterinarians to narrow differentials in many clinical settings. Thrombocytopenia can be easily diagnosed in any clinical setting. In this paper, we review the current understanding of primary hemostasis in veterinary medicine, including the clinical presentation and available diagnostics to identify platelet abnormalities.

Preliminary evaluation of a flow cytometric assay with microsphere controls for the detection of platelet-bound antibodies in canine immune thrombocytopenia

BACKGROUND

Canine immune thrombocytopenia (ITP) ranges from a mild to severe bleeding disorder, and platelet counts do not reliably predict clinical disease course. The detection of platelet autoantibodies may further define the disease phenotype, but variability in assay configurations and a lack of well-characterized controls limit the diagnostic utility of anti-platelet antibody assays.

OBJECTIVES

We aimed to develop control reagents to facilitate the characterization of canine platelet surface-associated immunoglobulin (PSAIg) in flow cytometric assays.

METHODS

Silica microspheres were coated with canine IgG and IgM to assess the reactivity of goat and rabbit origin anti-canine immunoglobulin reagents. They were also used as positive controls in the PSAIg assay. Preliminary assay evaluation and determination of sample stability used PRP isolated from seven healthy dogs and 26 dogs newly diagnosed with thrombocytopenia.

RESULTS

Blood sample stability was established for up to a 48-hour storage time. The conjugated positive control microspheres demonstrated stable fluorescent labeling over a 2-year observation period. Rabbit and goat origin anti-dog IgM fluorescent antibody labels reacted nonspecifically with canine IgG. Rabbit origin anti-dog IgG antibody demonstrated greater class specificity for canine IgG than a goat origin antibody. Thrombocytopenic dogs had a broad range of membrane-bound immunoglobulin. Median PSAIgG for dogs with primary or secondary ITP (18.4%, 34.1%, respectively) were significantly higher than controls (3.8%, P < .05).

CONCLUSIONS

The described assay reagents and procedures provide positive controls and allow consistent thresholding to define a positive test result, suitable for any flow cytometer. A rabbit anti-dog IgG fluorescent label demonstrated specificity for canine IgG and was useful for the detection of PSAIgG in thrombocytopenic dogs.

Exosomes as drug delivery vehicles and biomarkers for neurological and auditory systems

Exosomes are small extracellular membrane particles that play a crucial role in intracellular signaling. Research shows that exosomes have the potential to be used as biomarkers or drug delivery systems in specific organs, such as the neurological system and the inner ear. Exosomes in neurological and auditory systems release different molecules when under stress versus in healthy states, highlighting their potential use as biomarkers in the identification of diseased states. Studies have suggested that exosomes can be harnessed for drug delivery to hard-to-reach organs, such as cochlear sensory hair cells and the brain due to their ability to cross the blood-labyrinth and blood-brain barriers. In this article, we describe the biogenesis, classification, and characterization methods of exosomes. We then discuss recent studies that indicate their potential usage as biomarkers and drug delivery systems to help treat inner ear and neurological disorders.

Platelet number and function in response to a single intravenous dose of vincristine

Background

Vincristine might increase circulating platelet numbers but the functional capacity of these newly released platelets is unknown.

Objective

To evaluate and compare the functionality of mature and immature (reticulated) platelets after a single intravenous dose of vincristine in dogs.

Animals

Ten healthy purpose‐bred dogs.

Methods

Dogs prospectively received a single IV injection of 0.02 mg/kg vincristine or 0.9% saline. Before and after treatment on days 3, 5, and 7, platelets (resting and after thrombin stimulation) were assessed by flow cytometric determination of P‐selectin (CD62P) expression. Reticulated platelets were distinguished using thiazole orange (TO) staining.

Results

Relative to saline, vincristine administration increased platelet count from day 0 to day 7 (225 ± 58 to 273 ± 65 × 10³/μL, vs 299 ± 76.4 to 214 ± 20 × 10³/μL, P = .01) and increased percentage of reticulated platelets from day 0 to day 5 (3.9 ± 1.5% to 6.1 ± 1.6%, P = .02). On all days, reticulated platelets had greater resting expression of CD62P than did mature platelets (49.6 ± 4% vs 10.2 ± 1%, P ≤ .001). Across all days, CD62P expression by reticulated platelets in the vincristine and saline‐treated groups was not different when unstimulated (P = .7) or after thrombin stimulation (P = .33).

Conclusions and Clinical Importance

Reticulated platelets released in response to vincristine administration function similarly to mature platelets.

Abnormal platelet activity in dogs and cats - impact and measurement

Abnormal platelet activity can either lead to bleeding tendencies or inappropriate thrombus formation and can occur secondarily to a wide variety of disease processes, with a range of clinical consequences and severity. This article will discuss the pathophysiology of platelet function abnormalities and consider a logical diagnostic approach applicable to veterinary practice. Recent advances in platelet function testing will then be discussed, with regards to detection of platelet dysfunction and tailoring of pharmacological manipulation. Although many of these tests are still confined to research or academic institutions, techniques for indirectly assessing platelet function are starting to become more widely available. Although we still require further research to develop guidelines for the use of these tests in clinical decision-making, the recent advances in this field are an exciting step forward in being able to detect and manage platelet dysfunction in both primary care and referral practice.

Platelet Function and Therapeutic Applications in Dogs: Current Status and Future Prospects

Significant progress has been made in the functional characterization of canine platelets in the last two decades. The role of canine platelets in hemostasis includes their adhesion to the subendothelium, activation, and aggregation, leading to primary clot formation at the site of injury. Studies on canine platelet function and advancements in laboratory testing have improved the diagnosis and understanding of platelet-related disorders as well as the knowledge of the mechanisms behind these diseases. This review focuses on the most recent discoveries in canine platelet structure, function, and disorders; and discusses the efficacy of various tests in the diagnosis of platelet-related disorders. With the relatively recent discovery of angiogenetic and reparative effects of growth factors found in platelets, this review also summarizes the use of canine platelet-rich plasma (PRP) alone or in association with stem cells in regenerative therapy. The characterization of proteomic and lipidomic profiles and development of platelet gene therapy in veterinary species are areas of future study with potential for major therapeutic benefits.

Hemostatic function in Cavalier King Charles Spaniels assessed using thromboelastography

BACKGROUND

Macrothrombocytopenia is a well-known anomaly in Cavalier King Charles Spaniels (CKCSs), a breed also highly predisposed to develop myxomatous mitral valve disease (MMVD). Thromboelastography (TEG) has been shown to be a valuable instrument for whole blood hemostatic evaluation in dogs and correlates well with different physiologic and pathologic situations.

OBJECTIVES

We aimed to assess the influence of macrothrombocytopenia and the severity of MMVD on hemostatic function as measured by TEG.

METHODS

Associations between TEG variables (R, K, α, MA, and G) and dog characteristics, heart rates, systolic blood pressures, MMVD severities (healthy, mild or moderate, and severe), echocardiographic variables, platelet variables (platelet count, mean platelet volume [MPV], and plateletcrit), and hematocrits were evaluated in 47 prospectively recruited privately owned CKCSs. Blood samples were analyzed using a computerized thromboelastograph and an Advia 2120 hematology analyzer.

RESULTS

Univariable and multiple regression analyses showed an effect of left ventricular (LV) fractional shortening (FS%) on all TEG variables, an effect of LV FS% and age on TEG α, and an effect of LV FS% and MPV on TEG MA and TEG G. TEG MA and G increased with increasing MPV, but the associations were generally weak. No significant differences were detected in the TEG variables between the MMVD severity groups.

CONCLUSION

Macrothrombocytopenia and increased LV FS%, of which the latter commonly increases in various positive inotropic states, were both associated with a more hypercoagulable hemostatic system, according to the TEG results, in the present study.

A Remote Assay for Measuring Canine Platelet Activation and the Inhibitory Effects of Antiplatelet Agents

BACKGROUND

Antiplatelet medications are increasingly used in dogs. Remote analysis of platelet activity is challenging, limiting assessment of antiplatelet drug efficacy.

HYPOTHESIS/OBJECTIVES

To evaluate a method used in humans for stimulation and remote analysis of canine platelet activity.

ANIMALS

Forty-five dogs of various ages without a coagulopathy or thrombocytopenia. Six were receiving antiplatelet medication.

METHODS

Prospective observational study. Platelets were stimulated with combinations of arachidonic acid (AA) and epinephrine (Epi) or adenosine diphosphate (ADP) and the thromboxane A₂ -mimetic U46619 (U4). PAMFix was added to the blood samples to facilitate delayed analysis of platelet activity. Activity was assessed by flow cytometric measurement of surface P-selectin (CD62P) expression.

RESULTS

Canine platelets could be stimulated with both AA/Epi and ADP/U4. The levels of P-selectin were significantly greater than paired, unstimulated samples (P < 0.001). Inhibition of P-selectin expression occurred after this stimulation by adding antiplatelet drugs in vitro. The efficacy of antiplatelet drugs in samples from treated dogs was also measurable ex vivo using this method. Delayed analysis of platelet activity at time points up to 22 days demonstrated excellent correlation between respective mf values at each time point (r²  = 0.92, P < 0.0001).

CONCLUSIONS AND CLINICAL IMPORTANCE

This study evaluated a new method to remotely assess canine platelet activity. It shows that PAMFix can be used for this purpose. This provides opportunities to interrogate the inhibitory action of antiplatelet drugs in clinical settings.

Anoctamins/TMEM16 Proteins: Chloride Channels Flirting with Lipids and Extracellular Vesicles

Anoctamin (ANO)/TMEM16 proteins exhibit diverse functions in cells throughout the body and are implicated in several human diseases. Although the founding members ANO1 (TMEM16A) and ANO2 (TMEM16B) are Ca²⁺-activated Cl^- channels, most ANO paralogs are Ca²⁺-dependent phospholipid scramblases that serve as channels facilitating the movement (scrambling) of phospholipids between leaflets of the membrane bilayer. Phospholipid scrambling significantly alters the physical properties of the membrane and its landscape and has vast downstream signaling consequences. In particular, phosphatidylserine exposed on the external leaflet of the plasma membrane functions as a ligand for receptors vital for cell-cell communication. A major consequence of Ca²⁺-dependent scrambling is the release of extracellular vesicles that function as intercellular messengers by delivering signaling proteins and noncoding RNAs to alter target cell function. We discuss the physiological implications of Ca²⁺-dependent phospholipid scrambling, the extracellular vesicles associated with this activity, and the roles of ANOs in these processes.

A TMEM16F point mutation causes an absence of canine platelet TMEM16F and ineffective activation and death-induced phospholipid scrambling

BACKGROUND

TMEM16F is an ion channel and calcium-dependent lipid scramblase that mediates phosphatidylserine (PS) exposure on the plasma membrane. Two disparate disease phenotypes are associated with TMEM16F loss-of-function mutations: a rare bleeding disorder (Scott syndrome) and skeletal malformations due to aberrant bone mineralization in a TMEM16F knockout mouse. We therefore undertook comparative studies of TMEM16F expression in canine Scott syndrome (CSS), an autosomal recessive platelet defect.

OBJECTIVES

To define anoctamin proteins and scramblase response of CSS platelets and to determine whether TMEM16F is the CSS disease gene.

METHODS

CSS TMEM16F cDNA and gene were sequenced and mutation detection was performed in CSS pedigrees. Platelet fractions from CSS dogs were isolated for proteomic and immunologic characterization of TMEM16F. Annexin V was used as a flow cytometric marker of induced platelet PS externalization.

RESULTS

A TMEM16F splice site mutation segregated with the CSS trait and TMEM16F protein was undetectable in CSS platelet membranes; however, a second anoctamin, TMEM16K, was found. Proteomic analyses revealed a network of 32 proteins that differentially cosegregated with platelet plasma membrane TMEM16F. CSS platelets had profoundly impaired scramblase response to pharmacologic and physiologic agents that increase intraplatelet calcium and conditions that induce apoptotic and necrotic cell death.

CONCLUSIONS

CSS platelets represent a TMEM16F-null mutant model that demonstrates a central role for TMEM16F in mediating platelet PS externalization in response to activating and death signals. Platelet TMEM16F may prove a novel drug target for modulating platelet procoagulant activity and extending platelet life span.

Assessment of canine autologous platelet-rich plasma produced with a commercial centrifugation and platelet recovery kit

OBJECTIVES

To characterize the cellular composition (platelets, erythrocytes, and leukocytes) and confirm reproducibility of platelet enrichment, as well as determine the platelet activation status in the final product of a commercial platelet-rich plasma kit using canine blood.

METHODS

Venous blood from 20 sedated client-owned dogs was used to prepare platelet-rich plasma (PRP) from a commercial kit. Complete blood counts were performed to determine erythrocyte, leukocyte, and platelet numbers in both whole blood (WB) and resultant PRP. The WB and PRP samples from jugular (fast collection) and cephalic (slow collection) venipuncture were also compared. P-selectin externalization was measured in WB and PRP samples from 15 of 20 dogs.

RESULTS

This commercial kit produced an average percent recovery in platelets of 64.7 ± 17.4; erythrocytes of 3.7 ± 0.8, and leukocytes of 31.6 ± 10.0. Neutrophil, monocyte, and lymphocyte percent recovery was 19.6 ± 7.2, 44.89 ± 19.8, and 57.5 ± 10.6, respectively. The recovery of platelets from jugular venipuncture (59.7 ± 13.6%) was lower than from cephalic recovery (68.8 ± 19.1%). The mean percent P-Selectin externalization for WB, PRP, and PRP with thrombin was 25.5 ± 30.9, 4.5 ± 6.4, and 90.6 ± 4.4 respectively.

CLINICAL SIGNIFICANCE

Cellular reproducibility of this kit was confirmed and platelets were concentrated within autologous serum. Additionally, measurements of P-selectin externalization showed that platelets are inactive in PRP unless stimulated to degranulate.

Platelet activation in a population of critically ill dogs as measured with whole blood flow cytometry and thromboelastography

OBJECTIVE

To determine whether critically ill dogs had increased platelet activation and whether the proportion of activated platelets correlated with severity of illness.

ANIMALS

82 dogs in the intensive care unit of a veterinary teaching hospital and 24 healthy control dogs.

PROCEDURES

Flow cytometry with monoclonal mouse anti-human CD61 and CD62 antibodies in resting and ADP-treated samples and kaolin-activated thromboelastography were used to compare platelet activation in blood samples of critically ill and control dogs. Serum antithrombin, von Willebrand factor, fibrinogen, and activated protein C concentrations; prothrombin time (PT); and activated partial thromboplastin time (aPTT) were measured. Revised survival prediction index, acute patient physiology and laboratory evaluation, systemic inflammatory response syndrome, and multiple organ dysfunction syndrome scores were used to estimate severity of illness. Severity of illness scores and platelet activation measurements were compared with survival time and duration and cost of hospitalization.

RESULTS

Critically ill and control dogs had no differences in platelet activation for non-ADP-treated samples measured. Critically ill dogs had significantly increased platelet activation in response to 2, 6, and 10 μM ADP. Critically ill dogs had significantly increased maximum amplitude, α angle, and global clot strength and significantly decreased clot formation time. Critically ill dogs had significantly increased fibrinogen concentration, PT, and aPTT and significantly decreased antithrombin concentration. Survivors and nonsurvivors had similar flow cytometry and thromboelastography values. Three dogs developed macrothrombosis.

CONCLUSIONS AND CLINICAL RELEVANCE

In this study, critically ill dogs had hyperreactive platelets, which may have contributed to a high incidence of hypercoagulability in this patient population.

Current diagnostic trends in coagulation disorders among dogs and cats

The diagnostic workup to differentiate hemorrhage caused by vascular injury from a systemic hemostatic imbalance typically involves a combination of broad screening tests and specific assays. The characterization of 3 overlapping phases of primary hemostasis, secondary hemostasis, and fibrinolysis provides a simple diagnostic framework for evaluating patients with clinical signs of hemorrhage. New techniques such as flow cytometry, thrombin-generation assays, thrombelastography, and anticoagulant drug monitoring are under investigation for veterinary patients; however, their ability to improve diagnosis or treatment requires further study in clinical trials.

Flow cytometric detection and procoagulant activity of circulating canine platelet-derived microparticles

OBJECTIVE

To measure platelet membrane-derived microparticle (PMP) content and thrombin-generating capacity of canine plasma subjected to specific processing and storage conditions.

ANIMALS

31 clinically normal dogs (19 males and 12 females).

PROCEDURES

Citrate-anticoagulated blood samples obtained from each dog were centrifuged at 2,500 × g to isolate platelet-poor plasma (PPP), then PPP was centrifuged at 21,000 × g to isolate microparticle-free plasma (MPF) and microparticle-enriched plasma (MPEP). Whole blood and paired samples of fresh and frozen-thawed PPP, MPF, and MPEP were dual labeled for flow cytometric detection of membrane CD61 (constitutive platelet antigen) and annexin V (indicating phosphatidylserine externalization). Platelets and PMPs were enumerated with fluorescent, size-calibrated beads. Thrombin generation in fresh and frozen-thawed PPP, MPF, and MPEP was measured via kinetic fluorometric assays configured with low tissue factor and low phospholipid concentrations.

RESULTS

Initial centrifugation yielded PPP with < 0.5% the platelets of whole blood, with median counts of 413 PMPs/μL for males and 711 PMPs/μL for females. Sequential centrifugation resulted in a 10-fold concentration of PMPs in MPEP and virtually depleted PMPs from MPF. Thrombin generation depended on PMP content, with median endogenous thrombin potential of 0, 893, and 3,650 nmol•min for MPF, PPP, and MPEP, respectively. Freeze-thaw cycling caused significant increases in PMP counts and phosphatidylserine externalization.

CONCLUSIONS AND CLINICAL RELEVANCE

Canine PMPs were major determinants of thrombin-generating capacity; preanalytic variables influenced plasma PMP content. Processing conditions described here may provide a basis for characterization of PMPs in clinical studies of thrombosis in dogs.

Elevated coated-platelets in symptomatic large-artery stenosis patients are associated with early stroke recurrence

Coated-platelets are a subset of platelets with increased procoagulant potential observed upon dual agonist stimulation with collagen and thrombin. These prothrombotic platelets are elevated in patients with non-lacunar ischemic stroke and decreased in patients with spontaneous intracerebral hemorrhage compared to controls. We now investigated coated-platelet synthesis in patients with symptomatic large-artery stenosis and explored the association between coated-platelet levels and stroke recurrence at 3 months in this population. Coated-platelet levels were determined in 60 patients with either acute stroke or transient ischemic attack due to large-artery stenosis and 60 controls. Recurrent stroke incidence at 3 months was stratified by tertiles of coated-platelet levels and compared among groups using a log-rank test. Large-artery stenosis patients had significantly higher coated-platelet levels than controls (mean ± SD, 42.0 ± 15.5% vs. 29.4 ± 13.5%, p < 0.0001). The 3-month cumulative incidence of recurrent stroke was 41% for the highest, 6% for the middle, and 5% for the lowest tertile of coated-platelet levels (p = 0.0045). These results show that elevated coated-platelet levels in patients with symptomatic large-artery stenosis are associated with early stroke recurrence.

Clinical characterization of canine platelet procoagulant deficiency (Scott syndrome)

BACKGROUND

Platelet function defects are rare causes of bleeding diatheses; however, disease prevalence might be underestimated because diagnosis requires assessment of specific parameters of platelet activation.

OBJECTIVES

The goal of this study was to characterize the clinical presentation of canine Scott syndrome (CSS), an intrinsic platelet function defect first identified in a closed colony of German Shepherds (GSD).

ANIMALS

Eleven (n = 6 female) client-owned GSD affected with CSS that sought veterinary care for one or more episodes of abnormal bleeding.

METHODS

Retrospective review of all cases of CSS diagnosed through the Comparative Coagulation Laboratory at Cornell University between 2005 and 2011. The diagnosis of CSS was based on 2 measures of platelet procoagulant activity: serum prothrombin consumption and flow cytometric detection of platelet phosphatidylserine externalization after in vitro activation.

RESULTS

Postoperative hemorrhage was the most common sign of CSS, whereas petechiae were not found in any dog. Although most GSD responded to platelet transfusion, refractory epistaxis in 2 GSD was managed by nasal arterial embolization. The CSS trait was not restricted to a single pedigree of related GSD or to a single geographic region.

CONCLUSIONS AND CLINICAL IMPORTANCE

Unlike thrombocytopenia and platelet aggregation defects, petechiae and other capillary hemorrhage are not typical features of CSS. After preliminary screening to rule out more common causes of hemorrhage, CSS should be considered in the differential diagnosis of recurrent hemorrhage in GSD, and potentially other breeds of dog. Definitive diagnosis of CSS requires specific tests of platelet procoagulant activity.

Inherited platelet disorders

OBJECTIVE

To present the latest information on inherited platelet disorders in domestic animals.

DATA SOURCES

Research articles and reviews spanning 40 years available on PubMed.

HUMAN DATA SYNTHESIS

Information regarding inherited platelet disorders in people is plentiful and often descriptions of human conditions have led to the identification of similar disorders in veterinary species. There are exceptions, however, in which specific inherited platelet disorders were first described in animals with subsequent identification in people.

VETERINARY DATA SYNTHESIS

Many inherited platelet disorders have been documented in animals at the functional and molecular level and that information is presented in this review.

CONCLUSIONS

Much progress has been made in the past 20 years in the characterization of inherited platelet disorders in animals at the functional, biochemical, and molecular level. The study of inherited platelet disorders has greatly enhanced the understanding of platelet physiology and has led in some instances to the development of platelet inhibitory medications. Characterization of inherited disorders at the molecular level greatly facilitates diagnosis and identification of affected and heterozygous animals thus avoiding propagation of the defect by breeders. When used with available functional and biochemical diagnostic tests, it significantly enhances the quality of care and case management.

Defects in coagulation encountered in small animal critical care

Critically ill small animals are at risk for developing coagulation abnormalities. The processes of inflammation and coagulation are intertwined, and severe inflammation can lead to disturbances of coagulation. Severe coagulation dysfunction is associated with increased morbidity and mortality. Pathophysiology, diagnosis, and treatment of coagulation dysfunction are discussed. Defects in coagulation in small animal patients are complex and a consensus on diagnosis and treatment has yet to be reached.

Influence of treatment with ultralow-dose aspirin on platelet aggregation as measured by whole blood impedance aggregometry and platelet P-selectin expression in clinically normal dogs

OBJECTIVE

To evaluate the influence of treatment with ultralow-dose aspirin (ULDAsp) on platelet aggregation, P-selectin (CD62P) expression, and formation of platelet-leukocyte aggregates in clinically normal dogs.

ANIMALS

18 clinically normal dogs.

PROCEDURES

Studies were conducted before and 24 hours after ULDAsp administration (0.5 mg/kg, PO, q 24 h, for 2 days). Whole blood impedance aggregometry for the assessment of platelet function was performed with sodium citrate-anticoagulated blood and aggregation agonists (ADP at 20, 10, and 5 μmol/L; collagen at 10, 5, and 2 μg/mL). Onset, maximum response, and rate of platelet aggregation were recorded. Flow cytometric assays were configured to detect thrombin-induced CD62P expression and platelet-leukocyte aggregates in EDTA-anticoagulated whole blood. Externalized platelet CD62P and constitutive CD61 (GPIIIa) were labeled with antibodies conjugated to phycoerythrin (PE) and fluorescein isothiocyanate (FITC), respectively. Red blood cell-lysed paraformaldehyde-fixed EDTA-anticoagulated whole blood was dual labeled with CD61-FITC and a panleukocyte antibody (CD18-PE) to characterize platelet-leukocyte aggregates.

RESULTS

ULDAsp significantly delayed platelet aggregation onset with ADP at 20 μmol/L by 54% to 104%, attenuated maximum aggregation with various concentrations of ADP and collagen by ≥ 41%, and slowed aggregation rate with the highest ADP and collagen concentrations by ≥ 39%. Depending on the parameter tested, up to 30% of dogs failed to have an ULDAsp effect. Thrombin stimulation significantly increased CD62P expression in platelets and platelet-leukocyte aggregates, but ULDAsp did not alter basal or thrombin-stimulated CD62P expression.

CONCLUSIONS AND CLINICAL RELEVANCE

ULDAsp treatment of clinically normal dogs impaired platelet aggregation in most dogs, but did not influence CD62P platelet membrane expression.

Review of Continuing Education Course on Hemostasis

The continuing education course “Hemostasis” provided a comprehensive review of hemostasis and selected perturbations of the underlying processes as well as an assessment of hemostasis in animal models and preclinical testing environments. The session began with a review of the current state of understanding of hemostasis and how the waterfall or cascade of activation has transformed to the current cell-based, membrane-associated sequence of highly regulated events. The specific mechanisms of drug-induced thrombocytopenia were then presented, followed by a discussion of the relationships of coagulation and platelets in inflammation and cancer metastasis and platelet activity. Evaluation of hemostasis and platelet function in animals and especially in the environment of the contract research facility concluded the session.

Coated platelet levels correlate with bleed volume in patients with spontaneous intracerebral hemorrhage

BACKGROUND AND PURPOSE

Coated platelets are produced on dual agonist stimulation with collagen and thrombin. These highly procoagulant platelets are critical to normal hemostasis, and an earlier study demonstrated decreased coated platelet production in patients with spontaneous intracerebral hemorrhage. We have expanded this observation to investigate if coated platelet levels correlate with bleed volume in spontaneous intracerebral hemorrhage.

METHODS

Coated platelet levels and bleed volume were determined in 45 patients with a diagnosis of spontaneous intracerebral hemorrhage.

RESULTS

There was an inverse relationship between coated platelet levels and bleed volume (r=-0.38, P=0.01).

CONCLUSIONS

These data support a link between decreased coated platelet synthesis and the severity of spontaneous intracerebral hemorrhage.