Over thousands of years, greyhounds have been bred and selected for speed. This selective breeding may explain a number of the idiosyncrasies we see in the breed today. Retired racing greyhounds are becoming more common pets and more common patients in veterinary hospitals. It is estimated that about 18,000 greyhounds are placed into homes as pets annually. This article will familiarize practitioners with some idiosyncrasies in greyhounds that can affect their medical care.
COMPLETE BLOOD COUNT IDIOSYNCRASIES
Packed cell volume
It is well-known that greyhounds have a significantly higher packed cell volume (PCV) than other breeds (Table 1).1 Values are routinely above the upper reference range used by most laboratories.1,2 PCVs as high as 65% are not uncommon and are considered normal. PCVs less than 45% likely indicate some degree of anemia in a greyhound despite the fact that the value may fall within the reference range of most laboratories.
Table 1. Laboratory Values in Greyhounds and Other Dog Breeds*
Greyhounds have lower platelet counts than other breeds (Table 1).2 Reference values for greyhound platelets have been reported to be as low as 64,000/µl.3 One complicating factor in interpreting greyhound platelet counts is ehrlichiosis, a rickettsial tick-borne disease known to cause thrombocytopenia. In my opinion, a greyhound with a platelet count of 100,000/µl or less should be tested for ehrlichiosis and other tick-borne diseases. Protatek Reference Laboratory* provides discounts on serologic tests for tick-borne diseases in retired racing greyhounds. Symptomatic treatment of thrombocytopenia that includes doxycycline and, in some cases, corticosteroids can be considered.
White blood cell counts and morphology
Greyhounds routinely have lower white blood cell counts than other breeds (Table 1).1,3 Lymphocyte, neutrophil, and monocyte counts were all found to be lower in greyhounds than in nongreyhounds.3 These findings are rarely clinically relevant and are not necessarily indicative of immunosuppressive disease or overwhelming infection.
Greyhound eosinophils have empty granules and lack the more classic orange granules, making them appear vacuolated. This finding seems to be more common in slides stained with Diff-Quik (Dade Behring) than in those stained with Giemsa and can cause the eosinophils to be misidentified as toxic neutrophils.4
SERUM CHEMISTRY PROFILE IDIOSYNCRASIES
Creatinine and BUN concentrations
Greyhounds have significantly higher creatinine concentrations than other breeds (Table 1).5 These higher concentrations, primarily attributed to the breed's large muscle mass, often lead to a misdiagnosis of early renal disease. Female greyhounds have higher blood urea nitrogen (BUN) concentrations than other breeds.1 Greyhound glomerular filtration rates are similar to those of nongreyhounds (Drost WT, Couto CG, Fischetti AJ, et al., Department of Veterinary Clinical Sciences, The Ohio State University, Columbus, Ohio: Unpublished data, 2005). In dogs, raw food diets increase BUN concentrations and, in some cases, creatinine concentrations.6 Many active greyhound racers and some retired racers are fed a raw food diet, so their BUN and creatinine concentrations could be further elevated in the absence of renal disease.
Perform a urinalysis and measure urine specific gravity with a refractometer in any greyhound with a slightly elevated creatinine concentration. Absence of proteinuria and a urine specific gravity greater than 1.020 suggest that the creatinine concentration is likely normal for that particular patient.