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More on Platelet Function Testing

From Dave McGlasson:

George, Aquino in a recent article in CAP Today titled, “Puzzling out platelet function disorders,” posted July 6 on Fritsma Factor, extolled the virtues of light transmittance aggregometry [LTA] on platelet rich plasma [PRP] as the reference [“gold standard”] method to assess platelet aggregation disorders. This may have been true years ago but current whole blood aggregometry [WBA] on impedance-based platforms has been proven equal or superior in many ways to LTA. LTA uses optical density [transmittance] to measure platelet function in PRP prepared with low g-force centrifugation. The remainder of the specimen is recentrigued at a high speed to prepare platelet-poor-plasma [PPP] for a blank. Centrifugation requires at least 20 minutes of preparation time.

LTA is performed in specialized coagulation laboratories. In contrast, WBA may be offered as point-of-care testing [POCT] in many situations. In the article the author states that “you can test PRP by electrical impedance methods.”  However, I find no procedures that perform PRP testing by anything other than optical, where the instrument records rising transmittance as platelets aggregate, producing a platelet aggregatin curve.

WBA testing functions in a natural whole blood medium because red and white blood cells play a part in blood coagulation. Further, WBA is more fogiving to moderate thrombocytopenia.

I refer to two oft-cited articles that detail the uses of WBA listing advantages over LTA procedures:

McGlasson DL, Fritsma GA. Whole blood aggregometry and platelet function testing. Semin Throm Hemost 2009;35:168–80
Abstract: “Platelet aggregometry has been the reference method employed to detect, diagnose, and monitor qualitative platelet disorders since the early 1960s. Lumiaggregometry and impedance-based whole blood lumiaggregometry have advantages over light transmittance aggregometry in that they provide for enhanced specimen management and increase the test sensitivity to impairment of platelet granule secretion. Whole blood lumiaggregometry detects and identifies congenital and acquired platelet plasma membrane receptor defects, metabolic pathway secretion disorders, and storage pool deficiency. Whole blood lumiaggregometry is also being applied to antiplatelet therapy monitoring and identifies aspirin and thienopyridine resistance. There is growing interest in using impedance-based whole blood lumiaggregometry for near-patient whole blood platelet analysis and antiplatelet therapy monitoring. This article will also discuss other whole blood testing processes for assessing platelet function, particularly as applied to assessing the effect of antiplatelet medication.”

Fritsma GA, McGlasson DL Whole blood platelet aggregometry. In: Favaloro E, Lippi G (eds) Hemostasis and Thrombosis. Methods in Molecular Biology, 2017, vol 1646. Humana Press, New York, NY.
Abstract: “Light transmittance aggregometry is the historical reference method for platelet function testing and continues to be used extensively. Whole blood impedance lumiaggregometry represents an updated methodology that provides for simplified specimen management, an assay milieu that replicates in vivo platelet activation conditions, improved reproducibility, and near-patient testing. While the impedance-based whole blood aggregometer with luminescence channel is becoming the standard for platelet function testing using this methodology, at least three near-patient whole blood instruments are available, each employing its unique technology. We provide descriptions of whole blood lumiaggregometry and three near-patient systems. We include the principle of operation, materials, and stepwise example protocols and speculate on the importance of concordance among the platforms.”

Thank you, Dave McGlasson

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