Historical context is important, with recommendations to perform VWF:RCo assays in older guidelines “modernized” in latest VWD guidelines to preferential testing with either VWF:GPIbR or VWF:GPIbM (given the theoretically lower assay variability and better low VWF level sensitivity), with VWF:GPIbM “favored” since this should not yield false low values in patients with VWF mutations affecting ristocetin binding [15]. The gene discussed is VWF; the disease is von Willebrand disease (hereditary or acquired).