Introduction

Hemogram is the most requested blood test in routine laboratory because of its convenience, low cost and usefulness in clinical practice (Kerr 2003). May be required in different circumstances, among which to assess animals health status, help in diagnosis determination, to check body ability to support infections and evaluate the progress of certain diseases (Jain 1993), providing an instant overview of the hematopoietic system at a particular time, and to offer an overview on the state of the patient, because the peripheral blood serves as a very efficient means of transport for organic whole economy (Rebar et al. 2003). At the platelet analysis, one important analysis is the MPV (Mean Platelet Volume) because it represent a marker of platelet function, which is associated with indicators of platelet function, including aggregation, release of thromboxane A2, platelet factor 4 and beta-thromboglobulin, as well as power exchanges or reflect the level of platelets stimulation or the index platelets production (Henry et al. 1998). The plateletcrit (PCT) is the volume percentage that platelets match on a total volume of blood, and it is directly related to the total number of platelets (Moraes 2001). The platelet distribution width (PDW) is the width of the curve of distribution of platelets related to the different sizes produced by these cells. Like MVP, when the PDW is not normal shows the presence of some disorder in the production of platelets (Moraes 2001).

The mean platelet volume (MPV) is the estimated size of platelets and is inversely proportional to the number of platelets (Feldman et al. 2000). The increase of MPV occurs when there is an increase in turnover and consequent lack of platelet production in hyperthyroidism, myeloproliferative disease, idiopathic thrombocytopenia purpura, thrombotic thrombocytopenic purpura, disseminated intravascular coagulation, myeloproliferative syndromes (chronic myeloid leukemia, myelofibrosis) post-splenectomy, hyposplenia states, diabetes mellitus (Zago et al. 2004) and vascular disease characterized by pathological changes in blood vessels (Greisenegger et al. 2004). This is the first study in the Northern Region of Brazil.

Materials and Methods

This study was conducted from September to November 2008, in the cities of Belém, Ananindeua, and Marituba -Pará State, Brazil, which is predominant equatorial climate, with constant rain and directly influenced by the Amazon rainforest. 113 dogs (80 females and 33 males) of various breeds, and ages ranging from three months to 13 years from breeders, UFRA and military police Kennels were used. Before blood obtaining, animals were first selected by nutritional status followed by a history that included questions related to vaccination, presence of parasites and finally subjected to clinical examination to confirm the presence or absence of any clinical sign. That ones considered healthy were separated and identified for the blood sample collection. Blood samples were taken according the rules of the Research Ethics Committee of Laboratory Animals of the Institute Evandro Chagas. The 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 routinely techniques used in that laboratory (standard operating procedure), using Hematological Cell-Dyn 3700 analysis unit (ABX Diagnostic, Montpellier, France) showing a good performance and testing quality control during the daily analyses. PLT (platelet count per mm³), MPV (mean platelet volume by fL), PCT (in the percentage of occupied platelets in blood) and PDW (platelet range of variation) 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 PLT with PCT, PDW with PCT, MVP with PCT and PDW with MVP were positive while PLT with MPV and PLT with PDW were negative. All correlations were significant (P = 0.005). Values of correlations are shown on Table 2 and Figure 1.

Table 1. Pearson (above the diagonal) and Spearman's correlation (below the diagonal) between Canine Mass Body Indexes. Belém, 2009.

PLT = (Platelet Counts 10³/µL); MVP = (Mean Platelet Volume fL); PCT = (plateletcrit %); PDW= (platelet distribution width GSD). Reference interval (CV=95%)

Table 2. Values of the Pearson correlation for the parameters platelet count, mean platelet volume and platelet cell distribution width by the automatic analyzer Cell-Dyn 3700 (ABX Diagnostic, Montpellier, France) from blood collected from dogs in the cities of Belém, Ananindeua and Marituba in State Pará, Brazil during the months of September to November of 2008.

PLT = (Platelet Counts 10³/µL); MVP = (Mean Platelet Volume fL); PCT = (plateletcrit %); PDW= (platelet distribution width GSD). Reference interval (CV=95%)

Figure 1. Graphics showing the Pearson correlations from platelet parameters on blood from various breeds of dogs. The graphic 1 shown the positive correlation between PLT with MVP, graphic 2 PLT with PDW, graphic 3 PCT with PDW, graphic 4 MVP with PCT, graphic 5 MVP with PDW and graphic 6 PLT with PCT.

Discussion and Conclusions

Quantification of platelets is a well recognized tool for a great number of diseases diagnosis and their counting on automatic analyzers allows important assessment on platelets. The most important are plateletcrit (PCT), mean platelet volume (MPV) and platelet distribution width (PDW) (Wiwanitkit 2004). Results showed that the range of reference for PLT found in this study was 259. 04 to 303.97x 10³ / μL with the mean of 281.5 ± 120.6. This corroborates with the average found by Silva et al. (2007) by comparing the platelet count with conventional automatic meter, with an average of 280 x 10³ / μL. Yilamaz et al. (2008), before causing an experimental endotoxemia in dogs, found an average of 425 x 10³ / μL, above the value found in this work. In respect to the reference, and Stokol & Erb (2007) found the values of 179 to 483 x 10³ / μL, a magnitude greater than can be justified because 10% of animals showed 18% with thrombocytopenia and thrombocytosis. The Middle platelet volume is a variable related to biological function and platelet activity, increases and decreases of HGV become important because they may be related to specific pathology (Abid et al. 2007). In human medicine, reference range for MVP is between 6.5 to 9.5 fL for adults (Farias & Dal Bó 2008). Santos et al., (2008) studied platelets size in humans with vascular disease and found 8.7 μm³ (± 0.5) as reference value to MVP. In healthy dogs Yilamaz et al. (2008), found the value of 9.3 ± 0.5, while Waner et al, (1997) found a variation between groups of 9 to 11.1 μ³ to healthy dogs. Platelet media counts was 249,000 x 10³ / mm³. The MVP average found in this study was 13.27fL (12.53-14.00). According Boudreaux & Ebbe (1998) the mean for dogs is 7.2 fL. Reference range for PCT was -0.33-0.39 (M 0.36 ± 0.16), corroborating with data from Yilamaz et al. (2008) that found PCT values of 0.33 ± 0.01. PDW values 19.85-20.5 (M 20.16 ± 1.68) were slightly higher than that described by Yilamaz et al. (2008) whose average were 17.5. Increase in PDW value can justify MPV increase found in this study. Because it is relatively new parameters for Veterinary Medicine, the scientific literature is still scarce and there is no standard description for the parameters accurately assessed. There were no statistical differences between males and females so the values described here serve for both. Harvesting and processing of the sample must be done carefully and in a timely fashion, because anticoagulants use can interfere with cell population morphology. MPV and PCT, PLT and PDW have a strong positive correlation, indicating that these variables tend to increase when the other ones increases. Values found in this research will be the reference for dogs in the Amazon Region. New researches are necessary to let the data reliability higher.

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