The Effects of Storage Time at 2–8 Degrees Celsius on the Stability of von Willebrand Factor in Thawed, Platelet-Poor Plasma

Objective: To investigate VWF stability in thawed plasma by comparing immediately thawed samples with plasma stored at 2–8°C for 24–96 hours. Materials and Methods: Plasma from healthy subjects with normal coagulation times and VWF panels was stored at -20°C for one week. After thawing (at 0 hours), VWF:antigen (VWF:Ag), VWF:glycoprotein Ib binding assay (VWF:GPIbM), and VWF:collagen binding assay (VWF:CB) were assayed. The remaining plasma was stored at 2–8°C and assayed at 24, 48, 72, and 96 hours. Differences between levels at baseline and 24, 48, 72, and 96 hours were deemed significant when P was < 0.05. Results: Thirty-five samples were enrolled, with 25 from healthy subjects (VWF:Ag levels > 0.50 kIU/L). Median levels (interquartile range) were as follows: VWF:Ag = 0.91 (0.72–1.06) kIU/L; VWF:GPIbM = 0.85 (0.69–1.04) kIU/L; and VWF:CB = 0.78 (0.62–0.97) kIU/L. VWF:Ag remained stable for 72 hours, while VWF:GPIbM decreased significantly after thawing. VWF:CB declined after 48 hours at 2–8 °C. Similar stability trends were observed in 10 additional samples from VWD patients (VWF:Ag = 0.42 (0.36–0.46) kIU/L). Conclusion: VWF:Ag and VWF:CB are stable in thawed plasma for 72 hours. VWF:GPIbM is less stable and should not be kept longer than 24 hours. Immediate testing of VWF:GPIbM after thawing is recommended.