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Analytical Performance of a New Immunoturbidimetric Assay for von Willebrand Factor (VWF) Activity Testing by Susan Louw, Yuen O. Wan, Elizabeth S. Mayne, Johnny N. Mahlangu

Background: Von Willebrand disease requires laboratory confirmation with quantitative and qualitative measurements of von Willebrand factor (VWF). Qualitative VWF-activity (VWF-Ac) tests have poor inter- and intra-laboratory reproducibility with coefficients of variation (CVs) as high as 64%, often lacking accuracy at low VWF-Ac levels.
Methods: This study evaluated the recently launched immunoturbidometric STAGO® STA-VWF:RCo® reagent for VWF-Ac. Accuracy was evaluated on 32 samples by comparing results using the Siemens® Innovance® reagent. An intra-run reproducibility study was performed on controls. Linearity and lower limit of detection was studied on external-quality-assurance (EQA) material with a known VWF-Ac level.
Results: STA-VWF:RCo® reagent results were within clinical interpretation agreement with Siemens® Innovance®. The reproducibility study yielded % CVs of 8.41 for normal and 11.46 for abnormal controls and the assay was linear between 73 and 14.6% and remained linear to 2% with extrapolation.
Conclusions: The STAGO® STA-VWF:RCo® reagent showed clinically meaningful accuracy and acceptable precision.

DOI: 10.7754/Clin.Lab.2018.180919