Introduction

Nowadays veterinary medicine laboratory is following the human laboratory medicine modernization, using new equipments and techniques for diagnosis a great number of diseases that affect body systems. Hematological values can vary between domestic animals depending on their breed, age, sex, nutritional status, environmental conditions, behavioral changes, clinical status and methods for samples analysis (Allard et al. 1989; Lowest et al. 1993). Therefore, the quality and reliability of laboratory testing begin with selection and preparation of the patient, continues with collection and handling of the material, and finished with the analytical results (Meyer et al. 1995; Jain 1993). In the laboratory routine, automatics counters provide hematological additional information on the blood cell volume. Such equipment calculates the distribution of the red blood cells diameter, called RDW (Red Blood Cell Distribution Width) whose value reflects the heterogeneity degree among the cells through a quantitative analysis (Weiser et al. 1983). RDW is the coefficient of variation of red blood cells distribution volume and can be considered an index of heterogeneity, equivalent to anisocytosis observed in blood smear (Karnad & Poskitt 1985). The index most commonly used to assess the degree of anisocytosis is the mean corpuscular volume (MCV), which is typically calculated using date from volume and globular erythrocyte counts. However, many changes in the volume of these cells are not detected by examining only the MCV. A large percentage of cells with modified volume are required to produce a MCV abnormal red blood morphology, and evaluation to determine the presence of anisocytosis method is limited because of its subjectivity (Roberts & El Badawi 1995). This study was realized to determine RDW in dogs from northern region of Brazil. This is the first research using this kind of analysis in this Brazilian region.

Table 1. Reference interval values, means and standard deviation for the parameters RBC, RDW, MCV of blood samples from dogs collected during the month of September to November of 2008 in the region of Belém--Para State, Brazil. 2009.

RBC = (Red Blood Count 10⁶/µL); RDW = (Red Cell Distribution Width %); MCV = (Mean Corpuscular Volume fL). Reference interval (CV=95%)

Figure 1. The graphic 1 shown the positive correlation between RBC and RDW, and the graphic 2 describe the RDW x MCV correlation. These parameters were measured in blood samples taken from dogs during the month of September to November of 2008 in the region of Belém--Para, Brazil. 2009

Materials and Methods

This study was conducted from September to November 2008, in the cities of Belém, Ananindeua and Marituba, Pará State, Brazil. The prevailing climate in this region is equatorial, with constant rain and directly influenced by the Amazon rain forest. 113 dogs (80 females and 33 males) of various breeds were studied, ages ranging from three months to 13 years, from breeders, UFRA and military police kennels. After clinical examination, healthy animals were separated and identified and a blood sample was taken from jugular vein. The blood samples were taken according the rules of the Research Ethics Committee of Laboratory Animals of the Institute Evandro Chagas. Processing and analysis were done in Hematological Laboratory of Clinical Pathology "Amaral Costa", at Belém, Pará state, Brazil. All samples were processed at the same day of collection, following the techniques routinely used in that laboratory (standard operating procedure), using Analysis Hematological Cell-Dyn 3700 unit (ABX Diagnostic, Montpellier, France) showing a good performance and testing quality control during the daily analyses. RBC (Red Blood Cell Count), MCV (Mean Corpuscular Volume) and RDW (Red cell distribution Width) were evaluated. Results were compared between females and males (group 1 and 2) for the same variables using the analysis of variance by ONE WAY ANOVA statistical program--MINITAB. The averages were then compared by Tukey test at 5% probability. The different cellular parameters were also submitted to testing to verify a correlation of the presence of any linear association between the data.

Results

There was no statistical difference between females and males. The reference interval values (CI 95%), the mean and standard deviations are described in Table 1. The values of the Pearson correlation for RBC and RDW were positive (R2 = 0.0605) and significant (p < 0009) to RDW and MCV was also significant (p < 0022) but negative (R2 = 0.0462). The Figure 1 shows the respective correlations graphics.

Discussion and Conclusions

The statistical analysis showed no significant differences between males and females, with corroborating (Flaiban & Balarin, 2004). The values of RDW and MCV presented in Table 1 show that the value of MCV 69.19 ± 4.28 is similar as 68.8 ± 3.07, found by Neiger et al. (2002). The mean value of RDW (16.44 ± 1.41) is lower than of 17.5% like observed by Yilmaz et al. (2008) but it is within the values considered normal for dogs--14 to 19%--(Dunn, 2008; The Pet Center, 2008). The literature describes a wide variation in the values of RDW. Blood disorders are the main responsible for this enormous change in values. Studies such as Neiger et al. (2002) in normal dogs with regenerative anemia and not based on the parameter of regenerative RDW found the values of 15.6 ± 1.35 for normal dogs, 15.3 ± 3.93 for regenerative anemia and 16.2 ± 2, 78 for dogs with non-regenerative anemia. Perret et al., (2001) described in dogs with regenerative anemia, is greater or equal to 10, 9 to RDW in 46% of animals and this percentage was 66% of dogs that had a strong reticulosis. For these authors, anisocytosis occurs due to a mixture of "normal" red blood cells and reticulocytes whose volume is superior to another cell. This discrepancy between data in the literature can be justified by differences in breeds, conditions as the animals are created, methods of collection, physical exercise and sub-clinical disease. Although the values found in this work are mostly within the cited in the literature further studies in different regions should be undertaken. In conclusion, RDW is a parameter that is part of a set of data, and should not be interpreted individually, as with the MCV, RDW is important tool for anemia differential diagnosis and other systemic disorders. The average values found, can be used as parameters for both males and for females in this Region until additional studies can be realized.

References

1.  Allard RL, Carlos AD, Faltin EC. 1989.Canine hematology changes during gestation and lactation. Companion Animal Practice. 19:3-6.

2.  Lowseth LA, et al. 1993. The effects of aging on hematology and serum chemistry values in the beagle dog. Veterinary Clinical Pathology. 19: 13-19.

3.  Meyer DJ, Coles EH, Rich LJ. 1995. Medicina de laboratório veterinária: interpretação e diagnóstico. São Paulo. Roca. 308

4.  Jain NC. 1993. Essentials of veterinary hematology. Philadelphia. Lea & Febiger.

5.  Weiser G, Kohn C, Vachon A. 1983. Erythrocyte volume distribution analysis and hematologic changes in two horses with immune-mediated hemolytic anemia. Veterinary Pathology. 20: 424-433.

6.  Karnad A, Poskitt TR. 1985.The automated complete blood cell count--use of the red blood cell volume distribution width and mean platelet volume in evaluating anemia and thrombocytopenia. Archives of Internal Medicine. 145: 1270-1272.

7.  Roberts GT, El Badawi SB. 1995. Red cell distribution width index in some hematologic diseases. American Journal Clinical Pathology. 83: 226-236.

8.  Neiger R, Hadley J, Pferffer DU. 2002. Differentiation of dogs with regenerative and non-regenerative anemia on the basis of their red cell distribution width and mean corpuscular volume. Veterinary Record. 150: 431-434.

9.  Yilamaz Z, Eralp O, Ilcol YO. 2008. Evaluation of platelet count and its association with platetcrit, mean platelet volume, and platelet size distribution width in a canine model of enterotoxemia. Veterinary Clinical Phatology. 2. 37: 159-163.

10. Flaiban KKMC, Balarin MRS. 2004. Estudo comparativo entre a amplitude de variação dos eritrócitos (RDW--Red Blood Cell Distribution Width) e o Volume Globular (VG), Volume Globular Médio (VGM) e a presença de anisocitose em extensão sang'ínea em cães. Semina: Ciências Agrárias. Londrina. 2. 25:125-130.

11. Duncan JR, Prasse KW, Mahaffey E. 1994. Veterinary laboratory medicine. Lowa: Ames. 3. 300.

12. The Pet Center.Com. 2009. The internet animal hospital. Disponível em: http://www.thepetcenter.com/exa/nv.html. Access on January. 2009.

13. Perret D, Trumel C, Diquélou A, Dossin et O, Guelfi JF, Espie C. 2001. Service de médecine des carnivores domestiques. Laboratoire d'hématologie. Revue Méd. Vét. 7. 152: 549-554.