Evaluation of an automated platelet-based assay of ristocetin cofactor activity

A. S. Lawrie, I. J. Mackie, S. J. Machin, F. Peyvandi

Research output: Contribution to journalArticlepeer-review


von Willebrand's disease (VWD) is regarded as the most common congenital bleeding disorder, and although not available in all laboratories von Willebrand factor (VWF) activity is most frequently assessed as ristocetin cofactor (VWF:RCo). This test can be technically challenging, is subject to poor sensitivity (∼20IU dL-1 VWF:RCo) and has a high degree of inter- and intra-assay imprecision [coefficient of variation (cv)>25%]. We studied an automated assay using a combined fixed platelet/ristocetin reagent (BC von Willebrand reagent, Siemens Healthcare Diagnostics) on the CS-2000i analyser (Sysmex UK Ltd). Initially inter- and intra-assay imprecision was assessed. The automated method showed good day-to-day reproducibility and linearity of standard curves. This technique, also gave low intra- and inter-assay imprecision using commercial normal (cv-1 vs. 20IU dL-1 for aggregometry. Samples giving results within the aggregometry measurable range (n=50) exhibited good correlation with the automated technique (median 70IU dL-1, range 7-184IU dL-1; and 64IU dL-1, 6-138IU dL-1 respectively; R2=0.85). We subsequently compared 3 different batches of BC von Willebrand reagent, using a second group of normal subjects and VWD patients (n=35, 55-139IU dL-1 and n=30, -1). The CS-2000i results exhibited no clinically significant variation between batches (mean cv=7%). The automated VWF:RCo assay offers a more sensitive, reproducible, robust and less laborious alternative to standard aggregometry.

Original languageEnglish
Pages (from-to)252-256
Number of pages5
Issue number2
Publication statusPublished - Mar 2011


  • Ristocetin cofactor
  • Von Willebrand factor
  • Von Willebrand's disease
  • VWF:RCo

ASJC Scopus subject areas

  • Hematology
  • Genetics(clinical)


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