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McGlasson D. L.; Ledford, M.; Barna, L.; Best, H. A.; Hickman, J. R.
Blood Coagulation & Fibrinolysis: January 1997
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We investigated whether Hepchek™ heparin removal filters could remove residual platelets from platelet-poor plasma (PPP) without compromising samples for lupus anticoagulant (LA) testing. Furthermore we assessed what effect, if any, plasma filtration has on various clotting tests that form the foundation for LA testing. Citrated blood was obtained from 35 normal donors. Two sets of citrated tubes were processed in order to obtain PPP. Citrated blood was also obtained from a single donor to check the actual amounts of platelets removed by the Hepcheck™ filtration device. One set of PPP samples was filtered using the Hepchek™ filter device and the other was not processed, i.e. unfiltered. Prothrombin time (PT), activated partial thromboplastin time (APTT), and kaolin clotting time (KCT) were performed on both unfiltered and filtered samples that were tested immediately and after freezing at-70°C for 24 h. Platelet counts on the single donor's citrated plasma were dramatically reduced after filtration. PT and APTT values showed small but statistically significant differences between unfiltered and filtered plasmas whether these were fresh or frozen samples. However, these differences were not clinically significant. KCT data showed statistical and clinical differences between unfiltered and filtered plasmas whether fresh or frozen plasmas were used. In contrast, KCT values were similar if unfiltered, fresh plasmas or filtered, frozen plasmas were used. Coagulation factor assays for factors VIII, IX and X were performed on both sets of PPP samples after freezing to determine if the filtration device affected these levels and would as a result, compromise APTT based lupus testing. Factor IX levels demonstrated a loss of activity following use of the device but no change was observed in factor VIII or factor X. Von Willebrand factor antigen and function as well as multimer structure were not affected by the filtration device in 10 normal donors. Filtering plasmas of two donors with a history of an LA dramatically prolonged clotting times for APTT, Dilute Viper Venom Time, mixing studies, and STACLOT LA tests in comparison with unfiltered plasmas. The data indicate that plasma filtration using the Hepchek™ device does not adversely affect coagulation testing. Furthermore samples requiring testing for the lupus anticoagulant can be filtered and subsequently frozen and compare favorably with freshly processed samples.

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