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Presentation Details
| VWF Activity GPIbM Assay Kit Evaluation Julie I.Tange1, Dong Chen1, Rajiv K.Pruthi1, 2, Juliana Perez Botero1. 1Division of Hematopathology, Department of Laboratory Medicine, Mayo Clinic, Rochester, MN, USA.2Division of Hematology, Department of Medicine, Mayo Clinic, Rochester, MN, USA |
Abstract
Background: Laboratory diagnosis von Willebrand disease (VWD) requires assessment of von Willebrand factor antigen (VWF:Ag), platelet-dependent VWF activity, and factor VIII activity (FVIII). Recent guideline updates recommend the use of the VWF Glycoprotein IbM and IbR (VWF:GPIbM and VWF:GPIbR) and ristocetin cofactor (VWF:RCo); with the preference being VWF:GPIbM or VWF:GPIbR for their improved analytical performance. Our laboratory currently utilizes the HemosIL® VWF Activity (Instrumentation Laboratory, Bedford, MA) latex assay (VWF:Lx) and reflex to the VWF:RCo when appropriate; for which we have published extensive performance data; however, this assay is not classified as a platelet-dependent method under current guideline definitions. To align with updated recommendations, we undertook an evaluation of the INNOVANCE® VWF Ac kit (Siemens Healthineers, Germany), a VWF:GPIbM method. Objectives: To assess the performance characteristics for the VWF:GPIbM kit in comparison to the currently utilized VWF:Lx assay. Methods: The INNOVANCE® VWF Ac (VWF:GPIbM) assay was optimized on the ACL TOP 750 (Instrumentation Laboratory, Bedford, MA) platform with the VWF:Lx assay serving as the reference method. Accuracy was evaluated using deidentified waste and IRB-approved 3.2% NaCit plasma samples (n=51). Normal donor samples (n=20) were used for initial assessment of reference interval. Precision was assessed across 3 levels, tested in quadruplicate each day for 5 days. Analytical measuring interval was performed using 9 concentrations prepared through serial dilution of a high concentration plasma pool with factor diluent and performed in triplicate within one run. Blank (n=2) and low-level (n=2) samples were additionally evaluated in quadruplicate per day for 4 days to assess detection capability. Results: Accuracy was evaluated using both using linear regression analysis and % agreement between clinical diagnosis (composite classification based on physician review of laboratory data and clinical presentation) and GPIbM-based diagnosis (VWF:GPIbM result interpreted in conjunction with VWF:Ag and FVIII). Passing-Bablock regression demonstrated excellent concordance with the VWF:Lx, producing a slope of 0.989 and a correlation coefficient of 0.979, Figure 1. Figure 2 illustrates the % agreement findings. Of note, one patient sample recovered 52% VWF:Lx and <2% VWF:GPIbM with 23% VWF:Ag, <12% VWF:RCo, and multimer analysis had a visual loss of high molecular weight multimers. Clinically, the patient was confirmed to have acquired VWD. The reference interval yielded a range of 46-185%, with only one sample falling outside of laboratory’s current normal range (55-200%). Precision testing produced mean values of 104%, 25%, and 7%, with within-laboratory CVs of 1.0%, 3.0%, and 4.1%, respectively. The analytical measuring interval study resulted in concentrations ranging from 2-172% and an R2 of 0.999. Detection capability blank samples displayed a mean of <1% (SD 0.27) and low-level samples with a mean of 4% (SD 0.25); the calculated limit of blank was 1% and limit of detection was 2%. Conclusions: The INNOVANCE® VWF Ac assay demonstrated excellent performance characteristics on the ACL TOP 750 platform. However, because this represents a deviation from the FDA-cleared reagent-instrument combination, the responsibility for establishing sufficient validation to support clinical use rests with our laboratory.
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