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Platelet Neutralization Procedure

Geoffrey Wool, MD, PhD, Associate Director of Coagulation at the University of Chicago Medical Center Laboratory, provided an excellent Webinar, “Lupus Anticoagulant Testing: Managing Interferences and Optimizing Quality” on the Labroots provider site.

Dr. Wool addresses among other issues the time-honored platelet neutralization procedure (PNP), in which concentrated phospholipid extracted from platelets is used to neutralize a suspected lupus anticoagulant. PNP reagent, a “home brew,” may be used in the DRVVT or PTT system. Lupus anticoagulant is confirmed if either is shortened by 5–7 seconds.

Dave McGlasson, MS, MLS adds this comment. “I enjoyed your LA presentation on Labroots. I’d like to add that factor V deficiency causes a false positive PNP assay result. This is documented in McGlasson DL, Mercier RJ, Potempa L, Patterson WR. Platelet neutralization procedure (PNP): atypical results seen with a factor V deficiency with and without the presence of an inhibitor. Clin Lab Sci 1990; 3:119–21, in McGlasson DL. Platelet neutralization procedure and factor V inhibitors. (letter to the editor) Lab Med 2002; 33: 669, and McGlasson DL, Mercier RJ, Patterson WR, Potempa LF. Acquired factor V inhibitor with laboratory features of a lupus anticoagulant; case of the month1990; 3:4.

Dave also asked Dr. Wool to comment on normalization of DRVVT screen and confirmatory assays with reference to a report that recommends against normalization: McGlasson DL, Fritsma GA. Comparison of six dilute Russell viper venom time lupus anticoagulant screen/confirm assay kits. Semin Thromb Hemost 2013; 39:315–9.


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