INTENDED USE
The CHRONO-LOG® Ristocetin Cofactor Assay is for use in the quantitative determination of Factor VIII Ristocetin Cofactor activity in citrated plasma.
SUMMARY
Ristocetin Cofactor Activity in plasma may be determined by the agglutination of a standardized suspension of platelets in the presence of von Willebrand factor using the antibiotic Ristocetin.
1. The Ristocetin Cofactor Activity is the in-vitro activity of the von Willebrand factor which is responsible for the agglutination of platelets in the presence of Ristocetin. Although the platelets play a passive role in such agglutination there is an absolute requirement that the Ristocetin-dependent receptor be intact.
2. von Willebrand disease is associated with a decrease in von Willebrand factor or Ristocetin Cofactor activity and it is generally accepted that the Ristocetin Cofactor activity is the most useful in vitro assay for the diagnosis of von Willebrand disease.
3. Four Levels of Ristocetin Cofactor activity are determined by the ability of the test plasma and Ristocetin to induce aggregation in a standardized platelet suspension.
PRINCIPLE
Following reconstitution, the lyophilized platelets are treated with Ristocetin in the presence of dilutions of a normal standardized human plasma with known amounts of Ristocetin Cofactor activity. A standard curve is prepared, a patient plasma is then used as a source of Ristocetin Cofactor activity in the presence of Ristocetin and reconstituted platelets from which an aggregation pattern is determined and the Ristocetin Cofactor activity is interpolated from the standard curve.
