Ristocetin cofactor


4.5 mL blood added to 0.5 mL citrate.


Ristocetin-induced agglutination of fixed, washed platelets is dependent on added VWF.

Test and pooled normal plasma assayed in parallel dilutions.

Activity of test plasma expressed as % of activity in pooled plasma.

The reference assay is performed on a platelet aggregometer. Abbreviated VWF:RCo.

Reference Interval:

Refer to laboratory. Generally 50-200% of the activity in pooled normal plasma.


Additional functional VWF assay complimentary to the collagen binding assay in the investigation of possible bleeding disorder.

Diagnosis of von Willebrand disease and its variant forms, see von Willebrand disease testing.


See von Willebrand disease.


Favaloro EJ. Clin Haematol 2001; 14: 299-319.

Favaloro EJ. Haemophilia 2002; 8: 828-831.

McFarlane DE et al. Thromb Diath Haemorrh 1975; 34: 306.

Marder VJ et al. Thromb Haemost 1985; 54: 871-872.

Go Back

Page last updated:

Copyright © 2020 RCPA. All rights reserved.