by John Dillberger, DVM
Reprinted from the May/June 2013 Claymore.
At the 2012 National Specialty, researchers from The Ohio State University (OSU) collected blood samples from 96 normal, healthy Deerhounds. They analyzed the samples to measure various parameters in order to establish what are called “reference intervals” (RIs). RIs provide a range of normal results for a particular blood test.
The OSU group will publish this work in an upcoming issue of the Journal of Small Animal Practice. I my column this month, I summarize the OSU paper. I suggest that you keep a copy of the column for your own reference and also give a copy to your veterinarian.
Breeds that belong to the sighthound family have unique anatomical and physiological features that are presumably due to intentional selection for hunting by speed and sight. Consequently, it should not be surprising that blood test results for sighthounds often fall outside the established RIs for dogs in general.
Differences in RIs are well documented in Greyhounds. For example, the ratio between red blood cells (RBCs) and plasma is higher in the blood of Greyhounds than the blood of non-sighthound breeds. As a consequence, the RIs for blood tests that measure this ratio (hematocrit, hemoglobin concentration, and RBC count) are higher in Greyhounds than in dogs in general. The higher ratio reflects the fact that Greyhounds have more circulating RBCs, which improves oxygen delivery to tissues during times of peak demand, such as during a chase or race.
Researchers at OSU recently reported RIs for blood tests in Spanish Greyhounds, which are called Galgos. Galgos also had higher RIs for hematocrit, hemoglobin concentration, and RBC count than did dogs in general.
Limited information is available on RIs for blood tests in non-Greyhound sighthound breeds. The best studied RIs are for serum thyroid hormone concentrations, where low serum total T4 concentration has been reported in several sighthound breeds, including Deerhounds.
Materials and Methods
Blood samples were taken on May 10 and 11, 2012 from 96 Deerhounds (41 males and 55 females) from the USA and Canada whose owners signed a consent form to have their dogs included in the study. Dogs ranged in age from 6 months to 10 years, with an average age of about 3½ years. All dogs were considered healthy at the time of sample collection. Dogs were not intentionally fasted for any period of time before samples were collected.
Samples were handled, processed, and analyzed by routine methods that are described in the published paper. Whole blood was analyzed to measure the hematology parameters shown in Table 1 using an instrument called a Pro-Cyte Dx analyzer. Serum was analyzed to measure clinical chemistry parameters using an instrument called a COBAS c501 chemistry analyzer. The instrument measured concentrations of total thyroxine (T4), blood urea nitrogen (BUN), creatinine, phosphorous, total calcium, sodium, potassium, chloride, bicarbonate, cholesterol, bilirubin, total protein (TP), albumin, and glucose; and activities of the enzymes abbreviated as ALT, AST, ALP, GGT, and CK. These data were used to calculate anion gap, osmolality, globulin concentration, and albumin: globulin (A:G) ratio.
Due to small sample volume in some of the dogs, serum samples suitable for analysis were obtained from only 86 of the dogs. Of these, only 85 yielded useful results for ALP and GGT activities, only 81 yielded useful results for CK activity, and only 77 yielded useful results for total T4 concentration.
From 51 dogs in the study, blood smears were made immediately after collection, stained, and examined by light microscopy by a trained technician.
Hematology results are summarized in Table 1.
The majority of the RIs for hematology parameters were similar in Deerhounds and dogs in general, although the Deerhound RIs were narrower, as would be expected for a subpopulation of patients with similar characteristics. The major exception was the RI for platelets, where the RI for Deerhounds was substantially lower than for dogs in general; indeed, more than half the Deerhounds in this study had platelet counts below the RI for dogs in general.
Deerhounds also tended to have a greater MCV value than dogs in general; however, the majority of Deerhound MCV values were within the RI for dogs in general.
Clinical Chemistry Results
Clinical chemistry results are summarized in Table 2.
The majority of the RIs for clinical chemistry parameters were similar in Deerhounds and dogs in general, but with some exceptions:
• Calcium, where the RI was wider for Deerhounds than for dogs in general. The increased width was entirely on the low end; indeed, more than half of the Deerhounds in this study had serum calcium concentrations below the RI for dogs in general.
• Glucose, where the RI was lower for Deerhounds than for dogs in general. More than one in three of the Deerhounds in this study had serum glucose concentrations below the RI for dogs in general.
• Globulin, where the RI was wider for Deerhounds than for dogs in general. Almost one in three of the Deerhounds in this study had serum globulin concentrations below the RI for dogs in general.
• Chloride, where the RI was lower for Deerhounds than for dogs in general. More than one in four of the Deerhounds in this study had serum chloride concentrations below the RI for dogs in general.
• ALT, where the RI was higher and wider for Deerhounds than for dogs in general. Almost one in four of the Deerhounds in this study had serum ALT activities above the RI for dogs in general.
• BUN, where the RI was higher for Deerhounds than for dogs in general. Almost one in five of the Deerhounds in this study had serum BUN concentrations above the RI for dogs in general.
• Potassium, where the RI was slightly wider for Deerhounds than for dogs in general. The increased width was entirely on the high end; indeed, almost one in six of the Deerhounds in this study had serum potassium concentrations above the RI for dogs in general.
Blood Smear Results
Eosinophils were unusual in 22 dogs: they were vacuolated (grey) in 17 dogs and had vacuolated granules with a red-orange inclusion in the center in 5 dogs. Probably as a consequence of the unusual features of eosinophil granules in many Deerhounds, the instrument used to generate hematology data mistook some of the eosinophils for neutrophils and therefore under-counted eosinophils in 29 dogs. In 13 of these dogs, the instrument-generated eosinophil count was approximately half of the actual count as done by examination of a blood smear, and 10 of these dogs had vacuolated (grey) eosinophils.
Platelet clumping was noted to varying degrees in 12 dogs. This is not unusual and is an artefact of the blood sample collection procedure. Larger-than-usual platelets were noted in 6 dogs. Again, this can be a normal variation.
Deerhounds tended to have low platelet counts. This has previously been reported in Greyhounds, Galgos, Whippets, and several other sighthound breeds.
One possible reason for the low platelet counts in Deerhounds is that Deerhound platelets are “hyper-aggregable,” meaning they are more prone to stick together if handled roughly. This is true for platelets in Greyhounds. Platelet clumping was noted in blood smears from about one in four Deerhounds, supporting the possibility that Deerhound platelets are hyper-aggregable. On the other hand, some of the Deerhounds with platelet clumping visible in the blood smear had normal platelet counts.
Another possibility is that the low platelet counts in Deerhounds are an unavoidable consequence of having relatively high RBC counts. Studies in Greyhounds have shown that the higher the RBC count, the lower the platelet count. From this observation in Greyhounds, researchers have put forth something called the bipotential stem cell theory. Basically, the theory is that primitive cells in the bone marrow have to decide if they will differentiate into RBC precursors or megakaryocytes (platelet precursors). The more cells that opt for becoming RBCs, the fewer cells are available to become platelets.
So, do Deerhounds have high RBC counts? The results of this study suggest that they do, although not quite as high as Greyhounds. Based on the RI for RBC count in this study, a milliliter of Deerhound blood normally contains about 6½ to 9 million RBCs. Various publications report that a milliliter of Greyhound blood contains about 6½ to 9½ million RBCs, while a milliliter of blood from dogs in general contains about 5½ to 9 million RBCs.
It is worth noting that another way to tweak RBCs to increase oxygen delivery to tissues during times of peak demand is to increase the size of individual RBCs. Deerhounds and Greyhounds seem to have taken this second approach, too. The average volume of RBCs (mean cell volume, or MCV) is about 70.4 fL in Deerhounds and is reported to be about 74.5 fL in Greyhounds, while it is reported to be closer to 68 fL for dogs in general.
Deerhounds tended to have eosinophils with unusual granules, called vacuolated or grey eosinophils. Grey eosinophils have also been reported in Greyhounds, Italian Greyhounds, and Whippets. These eosinophils are not associated with clinical disease and seem to function normally. Proposed causes for the different appearance of these cells are altered proteins in the granules or a decrease in the pH inside the granules, resulting in less binding of the eosin stain. The clinical relevance of the grey eosinophils is the inability of automated analyzers to correctly count grey eosinophils.
Deerhounds tended to have high serum cholesterol concentrations. This not so for Greyhounds, where cholesterol concentration tends to be relatively low.
Deerhounds tended to have high serum ALT activities. This has been reported in several other sighthound breeds, but no explanation has been proposed for this difference. It is presumed to represent a physiological variation that has no clinical consequences.
Deerhounds tended to have low serum total calcium concentrations. This has been reported in several other sighthound breeds. Again, there is no explanation for this difference, and it may represent a true physiological variation that has no clinical consequences.
I want to thank all of the Deerhounders who took the time and effort to participate in this research project. As a club, we should take pride in our achievement. Many breeds with far greater numbers of dogs do not have published RIs for blood tests.
As I already said, I strongly suggest that you give a copy of this column to your veterinarian, in case s/he doesn’t have access to the version that will be published in Journal of Small Animal Practice.
Dr. John E. Dillberger, P.O. Box 2118, Nashville, IN 47448-2118 (812) 988-6175 John@Greymorn.com