Using a novel ELISA-based screening assay, researchers were able to correctly identify variant von Willebrand disease (vWD) phenotypes with 88 percent accuracy, according to a report published in Blood. This assay’s findings correlated with traditional clinical laboratory von Willebrand factor (vWF) assays, while also providing results more quickly than the current standard of phenotypic variant testing.
“This assay may provide a rapid diagnostic method for variant vWD,” Jonathan C. Roberts, MD, of the Blood Research Institute at the BloodCenter of Wisconsin and Medical College of Wisconsin in Milwaukee, and lead author of the study, told ASH Clinical News. “It also has the potential to be a lower-cost assay, since it tests multiple vWF activities on a single, widely used ELISA platform, compared with multiple variant vWF activity tests [that are] currently used.”
Dr. Roberts and colleagues developed an ELISA-based vWF multiplex activity assay that could rapidly discriminate vWF biology and assign phenotypes on a single testing platform. The ELISA assay was then tested in patients enrolled in the Zimmerman Program for the Molecular and Clinical Biology of von Willebrand Disease (ZPMCB-VWD) through eight primary centers in the United States.
A total of 160 patients were included, all of whom had pre-existing vWD diagnoses: 134 with vWD, 22 with hemophilia A, and four with type 3 vWD. Patients with diagnosed vWD were classified as:
- Type 1 (n=21)
- Type 1C (n=30)
- Type 2A (n=23)
- Type 2B (n=23)
- Type 2M (n=20)
- Type 2N (n=17)
vWF activity profiles were generated for each subject and interpreted by linear discriminant analysis (LDA; a method to determine a variant vWD diagnostic algorithm). A jackknife resampling technique was used to validate LDA estimates and predict performance in the general population.
Dr. Roberts and colleagues found that LDA was able to correctly assign variant vWD phenotype (vWD type 1C, 2A, 2B, 2M, or 2N) in 124 of 134 patients, or 92.5 percent of the time. Jackknife analysis applied to LDA correctly determined variant vWD phenotype in 118 of 134 patients, or 88.1 percent of the time. “Thus, this assay may correctly assign variant vWD phenotype in a population of subjects undergoing evaluation for ‘variant vWD,’” the authors concluded.
Variability studies conducted on four different days found that the assay also provided consistent results, with low intra-plate and inter-plate variability (coefficient of variation ranges = 4.7-6.2% [median = 5.2%] and 11.2-19.2% [median = 14.1%], respectively). However, the authors noted, “assay consistency would need additional evaluation if implemented across various laboratories.”
The researchers noted another potential limitation of this study: The results will need to be validated in a larger population, but implementing this assay on a larger scale would require batch-production of pre-coated ELISA plates, rather than the freshly coated plates that were used in this study.
“Our findings may prove to be an improvement in diagnosing variant vWD. Since it is a screening test, and has potential to lower costs, it may allow more patients to be screened for variant vWD,” Dr. Roberts added. “The method we used with this assay could potentially be combined with additional vWF tests, as more vWF physiologic activities continue to be discovered. It may change the way in which we perform laboratory evaluation for variant vWD.”
Roberts JC, Morateck PA, Christopherson PA, et al. Rapid discrimination of the phenotypic variants of von Willebrand disease. Blood. 2016 February 25. [Epub ahead of print]