Effects of Storage Time and Hemodilution on Canine Platelet Function
ACVIM 2008
M.H. Kim1,2; B. Jefferson1; S.A. Kruth2; R.D. Wood1
1Department of Pathobiology and 2Department of Clinical Studies, Ontario Veterinary College, University of Guelph
Guelph, ON, Canada

The ability to evaluate primary hemostasis can provide insight into the pathophysiology and management of a number of diseases that impair platelet function in dogs. Aggregometry is considered the gold standard assay for assessing platelet function; however, its clinical utility is limited. The Platelet Function Analyzer-100® (PFA-100) is a bedside point-of-care test, but its clinical utility remains to be tested thoroughly. According to manufacturer's guidelines, the PFA-100® requires hematocrits (Hct) greater than 0.35L/L and processing within 4 hours of collection, which can present logistical problems in the clinical setting.

Objectives of this study were: 1) Establish effects of different storage times on platelet function as determined by PFA-100® and aggregometry; 2) Establish effects of hemodilution on PFA-100® closure time (CT); and 3) Establish if addition of autologous packed red blood cells to anemic blood corrects PFA-100® CT.

Ten healthy mixed breed dogs were studied. To evaluate the effect of sample storage time whole blood was collected in 3.2% buffered sodium citrate and kept at room temperature until analysis. Collagen-ADP cartridges were used to assess CTs. Platelet aggregation was measured using a Chrono-log® Model 440 dual channel optical aggregometer with two agonists: ADP (5x10-5mM) and platelet activating factor (1x10-7mM). To assess the effects of hemodilution on CT, each animal's own platelet-rich plasma was added to their whole blood in vitro to establish Hct values of 0.35, 0.25 and 0.15 L/L. Autologous packed RBCs were transfused into the 0.15 L/L dilutions with a goal of establishing a hematocrit of 0.45 L/L. CTs were measured for both hemodiluted and Hct restored samples using collagen-ADP cartridges.

PFA-100® closure times were not significantly different at times 0, 90, 120, 240 and 360 min (P=0.20). Similarly, aggregometry did not show any significant changes among comparisons at 90, 120, 240 and 360 min (all P values >0.05). Hemodilution of blood with autologous platelet-rich plasma resulted in significantly different PFA-100® CTs among whole blood, 0.35 L/L, 0.25 L/L and 0.15 L/L hematocrit values (P<0.05). The addition of autologous packed red blood cells significantly lowered the CT (P<0.01) and restored it into the reference range.

We conclude that: 1) Sample storage time of up to six hours does not significantly alter platelet function as assessed by PFA-100® and aggregometry testing; 2) Serial hemodilutions result in prolongation of PFA-100® closure time; and iii) Addition of autologous packed red blood cells into hemodiluted samples resulted in restoration of PFA-100® closure times to within reference intervals.

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Michael Kim

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