Page 1389 - Small Animal Internal Medicine, 6th Edition

CHAPTER 83 Clinical Pathology in Greyhounds and Other Sighthounds 1361

contrast with 60.6% in all other breeds combined; 2.9% had as thrombocytopenia and clotting factor or vWF deficiencies
DEA 1.2 antigen (versus 0 in other breeds). Almost two unlikely causes of the bleeding.
VetBooks.ir thirds (63.4%) of the Greyhounds were considered universal Dade Behring, West Sacramento, CA) to investigate primary
When using the PFA-100 (platelet function analyzer;
donors in contrast with 18.2% in the other breeds (Iazbik
et al., 2010). In contrast, approximately 50% of Galgos Espa-
times (CTs)—the time required for a platelet plug to form in
ñoles (Spanish Greyhounds) are positive for DEA 1.1 antigen. hemostasis, healthy Greyhounds had shorter mean closure
the capillary aperture and halt blood flow—than the non-
LEUKOCYTES Greyhound group; however, CT ranges were similar to
Previous studies reported lower mean white blood cell reported values for other dog breeds (Couto et al., 2006).
(WBC) counts in Greyhounds compared with other breeds. Surprisingly, the lower platelet counts observed in the breed
As noted, adult Greyhound RIs have been established for were not associated with prolongation of the CT; the shorter
total WBC, neutrophil, and lymphocyte counts (Campora CTs in Greyhounds are likely explained by the higher PCV,
et al., 2011). In most Greyhounds, eosinophils lack the and thus viscosity, in the breed. A higher PCV and whole
typical orange/pink granules when using Wright-Giemsa or blood viscosity lead to peripheral platelet distribution and
rapid hematology stains. These atypical eosinophils may be consequent increased interaction with the blood vessel
mistaken for toxic neutrophils on a routine blood smear surface. Shorter CTs in the breed may be an adaptive platelet
stained with Diff-Quik, leading to an unnecessary search for response to accommodate higher shear in Greyhounds
a source of infection (Iazbik et al., 2005). These gray eosino- because Greyhounds also have significantly higher arterial
phils also occur in some other sighthound breeds, such as blood pressure and aortic velocity than non-Greyhounds.
Whippets, Scottish Deerhounds, and Italian Greyhounds but Thromboelastography (TEG) allows for the evaluation of
are uncommon in Galgos Españoles. blood coagulation via assessment of the speed and strength
of clot formation. TEG is dependent on the function of the
PLATELETS primary and secondary hemostatic systems and fibrinolysis,
Greyhounds have lower platelet concentrations (PLT) than all of which can be affected by certain illnesses, environmen-
dogs of other breeds (Zaldívar-López et al., 2011a). The stem tal conditions, and pharmacologic agents. It was found that
cell competition model of hematopoiesis has been proposed Greyhounds have slower clot kinetics and weaker clot
as a possible mechanism for the low platelet count observed strength when compared with non-Greyhounds (Vilar et al.,
in Greyhounds, suggesting that bipotential stem cells within 2008).
the bone marrow are programmed to become megakaryo- Mechanisms of postoperative bleeding have been investi-
cytes or erythrocyte precursors. gated in retired racers; it was found that approximately one
Other proposed mechanisms for low platelet counts in in four Greyhounds has moderate to severe bleeding 36 to
Greyhounds include splenic or pulmonary sequestration or 48 hours after routine gonadectomy (Lara-Garcia et al.,
a chronic, low-grade, immune-mediated process leading to 2008). Numerous parameters were used to evaluate primary
decreased platelet life span. Anecdotally, platelets tend to and secondary hemostasis preoperatively—platelet count
clump more in Greyhounds than in other breeds, behaving (PLT), OSPT, aPTT, platelet function using the PFA-100,
more like feline platelets. Therefore in-depth investigation of fibrinogen (FIB), D-dimer, plasminogen, antiplasmin (AP),
a potential underlying cause of thrombocytopenia is not nec- antithrombin (AT) levels, vWF concentration (vWF Ag),
essary in healthy Greyhounds with moderate decreases in vWF collagen binding assay (vWF CBA), and factor XIII
platelet count (<100,000/µL). assay. Hemostasis assays were repeated in RRGs that devel-
oped bleeding complications at the time of the event, and in
an age- and sex-matched control group of RRGs that under-
HEMOSTASIS went the same surgical procedures at the same time and did
not bleed. Results from this study suggest that excessive post-
The main function of the hemostatic system is to keep the operative bleeding in RRGs is not attributable to a primary
blood flowing within the cardiovascular system. The term or secondary hemostatic defect but may be related to altered
Greyhound bleeder was proposed to describe dogs that tend fibrinolysis; the bleeders had lower AP levels than non-
to bleed spontaneously following minor trauma or after a bleeders preoperatively, suggesting activated fibrinolysis and
simple surgical procedure (Lara-Garcia et al., 2008). Severe a hypocoagulable state.
postoperative bleeding 1 to 4 days after limb amputation for
osteosarcoma or trauma has also been reported in Grey-
hounds, often resulting in the need for blood component CLINICAL CHEMISTRY
therapy during the postoperative period. Historically, Grey-
hounds with spontaneous bleeding have had normal platelet Several studies reported differences in specific serum bio-
counts for the breed, von Willebrand factor (vWF) concen- chemical values in Greyhounds when compared with those
tration, one-stage prothrombin time (OSPT), and activated of the general canine population. Veterinarians working
partial thromboplastin time (aPTT) at the time of postopera- with Greyhounds must consider these breed-specific differ-
tive hemorrhage, making common bleeding disorders such ences when interpreting serum chemistry profiles because