Development of a simple collagen based ELISA assay aids in the diagnosis of, and permits sensitive discrimination between Type I and Type II, von Willebrand??s disease
We have developed and evaluated an ELISA-based collagen binding assay (CBA) as an aid in the diagnosis and classification of von Willebrand's disease (vWD). The assay is simple to perform, and appears capable of differentiating Type U vWD from Type I vWD. Using plasma samples from both affected and non-affected patients, or from normal individuals, data obtained using the CBA were directly compared to data simultaneously derived from a standard von Willebrand factor antigen (protein; vWFAg) ELISA, and from a standard ristocetin cofactor (RCof) assay- Plasma derived from vWD patients (both Type I and Type II) showed overall reduced levels of vWF as detected by all three assays. Mean levels as a per cent of normal for vWFAg, CBA, RCof were 47.3, 60.7, 31.1 for Type 1 patients (n = 37), and 34.9, 1.6, 11.9 lot Type II patients (n = 16) respectively. However despite the reduced vWF levels detected in Type I vWD patients, vWF binding values for both the CBA and vWFAg showed near comparability (i.e. vWFAg:CBA ratio generally ≤ 1.0). These ratio values were thus similar to those observed using plasma derived from either individual normal donors, or from non-vWD affected patients. On the other hand, plasma from Type II vWT affected patients showed markedly disparent values, with increased (> 8.0) vWFAg:CBA ratios coincident with virtually absent CBA binding in these patients. Thus, the CBA as reported here does appear to constitute a novel functional assay capable of detecting qualitative vWF differences in plasma of affected vWD patients. Its simplicity makes it an ideal assay for any laboratory current investigating vWF or vWD patients, and may allow the future discovery of new dysfunctional forms of vWF in affected patients.