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.