Choices Ristocetin cofactor (VWF:RCo) Collagen binding assay (VWF:CB) VWF activity immunoassay (VWF:Act) Ristoectin-triggered recombinant GP Ib immunoassay (VWF:GPIbR) Non-ristocetin gain of function GP Ib immunoassay (VWF:GPIbM) CAPTCHAPlease confirm you are a human visitor to prevent automated spam submissions.