Severity of type 1 von Willebrand disease (VWD) may not be detectable using whole blood ristocetin-induced platelet agglutination (WB-RIPA), according to research published in Haemophilia.

Detecting type 1 VWD and classifying its severity can be difficult due to the varied presentations of this partial deficiency of von Willebrand factor (VWF).

Researchers examined a WB-RIPA assay in 55 patients with type 1 VWD and 20 healthy control subjects. The assay gave results in arbitrary aggregation units (U).

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The intent of the study was to unmask any associations between WB-RIPA values and VWF ristocetin cofactor (VWF:Co) and antigen (VWF:Ag) activity or bleeding tendencies in these patients. VWF:RCo and VWF:Ag were measured using standard laboratory assays, and a questionnaire was used to derive scores for bleeding symptom severity.

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WB-RIPA values differed significantly between the patient groups. Patients with type 1 VWD showed WB-RIPA values of 20.0 U (interquartile range [IQR], 10.5-62.5), compared with 107.5 U (IQR, 89-131; P <.0001) for healthy controls.

The researchers also determined that type 1 VWD could be diagnosed from a receiver-operating characteristics curve analysis of WB-RIPA results, with a threshold of 0.90 for the area under the curve.

Measurements of the VWF-related factors showed a strong correlation with each other (correlation coefficient r = 0.92), but they showed weaker correlations with WB-RIPA values (r = 0.22 with VWF:RCo; r = 0.28 with VWF:Ag). Bleeding score severity showed significant associations with levels of both VWF-related factors but not with WB-RIPA values.

Although the study demonstrated the WB-RIPA assay’s potential as a diagnostic tool for type 1 VWD, the lack of correlation with bleeding scores suggested that the assay may not be helpful in determining clinical severity.

Furthermore, the study authors stated “that the whole blood ristocetin‐based technique would be unlikely to add to the information derived from conventional measurements of VWF:Ag and Factor VIII activity.”


  1. Nakajima Y, Nogami K, Yada K, et al. Whole blood ristocetin-induced platelet impedance aggregometry does not reflect clinical severity in patients with type 1 von Willebrand disease [published online March 13, 2019]. Haemophilia. doi: 10.1111/hae.13725