Platelet parameters from an automated hematology analyzer in dogs with inflammatory clinical diseases

Abstract

The mean platelet component (MPC) is a proprietary algorithm of an automated laser-based hematology analyzer system which measures the refractive index of platelets. The MPC is related linearly to platelet density and is an indirect index of platelet activation status. Previous investigations of canine inflammatory conditions and models of endotoxemia demonstrated a significant decrease in the MPC, consistent with platelet activation. The purpose of this study was to evaluate the MPC and other platelet parameters in dogs with different diseases to determine if they could show differential platelet activation with different pathologies. The hypothesis was that the MPC would decrease in clinical conditions associated with systemic inflammation or platelet activation. Complete blood counts run on the analyzer from dogs with different inflammatory conditions (primary immune-mediated hemolytic anemia (IMHA) or thrombocytopenia (ITP), pituitary-dependent hyperadrenocorticism, intra-abdominal sepsis, pancreatitis, intravascular thrombus or thromboembolus and hemangiosarcoma) were reviewed retrospectively and compared with those of control dogs presenting for orthopedic evaluation.

Dogs with ITP had a decreased plateletcrit and MPC, with an increased platelet volume and number of large platelets (P < 0.001). Dogs with IMHA had an increased plateletcrit and mass, and more numerous large platelets (P < 0.001).With the exception of the ITP group, there was no difference in MPC in the diseased groups when compared with the controls. The results of this study suggest the MPC does not change in certain canine diseases associated with systemic inflammation.

Introduction

Platelet activation during systemic inflammatory conditions may contribute to the development of macro- or micro-thrombi, which can result in significant morbidity and mortality in hospitalized patients (Christopherson et al, 2012, Wiinberg et al, 2012, Kidd, Mackman, 2013). There is therefore interest in monitoring the platelet activation status in hospitalized patients. Early detection of patients at risk of thromboembolism might allow initiation of thromboprophylaxis and monitoring of the response of platelets to these therapies. Flow cytometric detection of activation markers and platelet microparticles has been described in dogs, but has not been extensively studied in a clinical setting (Moritz et al., 2003).

The automated ADVIA 120 Hematology System (Bayer Corporation) uses two-dimensional (2D) laser technology to identify and characterize the size and complexity of cells in EDTA-anticoagulated whole blood. The two light scatter signals generated by each platelet are converted into multiple parameters that represent the number, size, and complexity of platelets in humans (Table 1) (Macey et al, 1999, Giacomini et al, 2001). Similarly, the laser technology also allows canine platelets to be distinguished from erythrocytes and generates an accurate platelet count (Welles et al., 2009). The mean platelet volume (MPV) is a measure of the mean platelet size, while the platelet distribution width (PDW) indicates the variation in platelet size and the plateletcrit is the product of the platelet count and MPV, representing the percent of a deciliter of blood occupied by platelets (similar to hematocrit for erythrocytes). The mean platelet component (MPC) is a measure of the refractive index of platelets and is related linearly to platelet density (Barer et al., 1953), generating an indirect index of the platelet activation status (Thompson et al, 1982, van Oost et al, 1983, Corash, 1990, Zelmanovic, Hetherington, 1998). Once activated, platelets release procoagulant substances from alpha and dense granules, reducing platelet density, and therefore decreasing the MPC (Chapman et al., 2003).

Reference values for canine platelet parameters using the ADVIA 120 analyzer have been established by Moritz et al. (2004). Since then, studies have evaluated the effect of storage (Furlanello et al, 2006, Prins et al, 2009), anticoagulants (Stokol and Erb, 2007), and hemolysis (Bauer et al., 2010) on ADVIA platelet parameters. Some studies have also evaluated canine platelet parameters in response to experimentally-induced and spontaneous inflammatory diseases (Moritz et al, 2005, Rafaj et al, 2005, Yilmaz et al, 2008, Flatland et al, 2011).

The purpose of this study was to evaluate platelet parameters in dogs with a large number of disease states that are generally associated with systemic inflammation, and to compare them with a control series of dogs presenting for elective orthopedic surgery. Our hypothesis was that the MPC would be lower in clinical conditions thought to cause platelet activation.