Here are the results of our January, 2018 Quick Question.
Stem: What method do you use to measure von Willebrand factor activity?
a. Ristocetin cofactor (VWF :RCo): 61% (32)
b. Collagen binding assay (VWF :CB): 6% (3)
c. VWF activity immunoassay (VWF :Act ): 23% (12)
d. Ristoectin-triggered recombinant GP 1b immunoassay (VWF :GPIbR): 4% (2)
e. Non-ristocetin gain of function GP 1b immunoassay (VWF :GPIbM): 6% (3)
Total votes: 52
Thank you for participating in the survey. It appears the collagen binidng assay, which has been available since early in the 1990s, has gained little traction. While the ristocetin cofactor, collagen binding assay, and VWF activity immunoassay are familiar to most of us, here are excerpts from the draft for the sixth edition of Rodak's Hematology, which will be published later in 2018, explaining the ristocetin-triggered recombininat GP 1b immunoassay and the non-ristocetin gain of function GP 1b immunoassay:
For answer d: The VWF :RCo has been successfully automated, but has been partially replaced by automated ristocetin-triggered non-platelet recombinant GPIb-based LIA and CLIA methods such as the HemosIL AcuStar VWF :GPIbR (IL-Werfen, Bedford, MA), which the International Society on Thrombosis and Haemostasis Standardization Subcommittee (ISTH-SSC) for von Willebrand factor labeled VWF :GPIbR in their 2014 annual minutes.
For answer e: A promising alternative to VWF :RCo and VWF :GPIbR is an assay that incorporates a gain-of-function high affinity recombinant GPIb protein that resembles the GPIb of PT-VWD platelets. The GPIb binds the A1 domain of native VWF without the need for ristocetin. This assay has been commercialized as a LIA ; Innovance VWF Ac (Siemens Healthcare Diagnostics, Inc., Deerfield, IL ), and it appears to improve on ristocetin-based assays as it offers smaller VWF detection limits and less variability. The 2014 ISTH-SSC terms this assay VWF :GPIbM.