Platelet function analyzer‐200 closure curve analysis and assessment of flow‐obstructed samples

Abstract

BackgroundThe Platelet function analyzer‐200 can determine the effect of clopidogrel in cats. Flow obstruction is an error that causes uninterpretable results. Closure curves and parameters initial flow rate (IF) and total volume (TV) are displayed by the PFA‐200 and may allow interpretation of results in cases of flow obstruction. The primary hemostasis components (PHC) are calculated values that normalize these parameters.ObjectivesTo determine if closure curves and research parameters allow detecting the effect of clopidogrel in cases of flow obstruction.MethodsA review of closure curves identified those with flow obstruction and paired analysis that did not. Non‐flow–obstructed curves were used to categorize curves with respect to clopidogrel effects. IF, TV, PHC(1), and PHC(2) were evaluated to determine if these could be used to categorize if a sample exhibited the effects of clopidogrel. Curves were visually analyzed, and characteristics identified that were more common with or without the effect of clopidogrel. Visual analysis of curves was performed by blinded observers to determine if a visual analysis was able to predict the effect of clopidogrel.ResultsAnalysis of parameters was able to predict closure or non‐closure in flow‐obstructed curves. TV, PHC(1), and PHC(2) had area under the curve of the receiver operating characteristics of 0.79, 0.79, and 0.87. Visual curve analysis was unable to predict closure, with an average accuracy of only 55%, among three reviewers. Agreement between reviewers was poor (Fleiss' Kappa 0.06).ConclusionsVisual curve analysis was unable to determine the effect of clopidogrel in flow‐obstructed samples. Numerical parameters were able to detect the effect of clopidogrel with a high degree of accuracy in flow‐obstructed samples.

Determination of clopidogrel effect in cats using point-of-care Plateletworks ADP and shipped samples for PFA-200 analysis in a clinical practice setting

“…Of all samples collected, 86–90% were able to have the clopidogrel effect determined with any given assay, and all samples were able to have the clopidogrel effect determined using at least one of the three assays. Previous studies in our laboratory using point-of-care analysis within 4 h of sample collection had shown the rate of flow obstruction with the PFA-200 to be in the range of 10–20%, 4 , 5 comparable with the results seen in this study.…”

“…If duplicate flow obstructions occurred, closure curve and primary hemostasis component analyses were performed as previously described to determine the clopidogrel effect. 4 …”

“… 2 , 3 With respect to the latter, this is variably referred to as ‘clopidogrel resistance’ or ‘high-on-treatment platelet reactivity’, a situation in which platelets aggregate or react to agonists at a normal level, despite antiplatelet therapy. 3 – 6 Clopidogrel resistance is difficult to precisely define as the drug dose needed to prevent thromboembolism for a specific condition in a specific species may not be known, and it is not known if the level of inhibition seen on platelet function assays correlates with clinical outcome.…”

“… 2 , 7 Based on platelet function tests, ineffectiveness of the drug has been described in 15–20% of cats, though often with small sample sizes. 3 – 5 , 8 – 10 Determining which patients are resistant has until recently been difficult outside of specialized practices due to the requirement for testing to be performed within hours of sample collection, preventing the analysis of samples shipped from other locations. 5 , 9 …”