Register Login

Automated Ristocetin Cofactor

Here is a question I received early in January from Elpidio Pena. I apologize to Elpidio for letting this one slip through the cracks.

George: our lab performs the ristocetin cofactor (VWF activity) assay using the traditional platelet aggregation method. We are planning to change instruments and one of the instruments we are considering performs the assay by ELISA (coated beads). Any advantages/disadvantages on the ELISA method? Any particular issue to consider with this method?

Elpidio Pena

Thank you, Elpidio. You don’t identify the instrument you are considering, however Instrumentation Laboratory (IL) is promoting their latex assay, which has accumulated some favorable data from several sources. Do any of our subscribers have experience to share?

Comments (2)
Apr 12, 2010 8:38am

Many thanks to Dr. Favaloro for this helpful clarification.
Many thanks to Dr. Favaloro for this helpful clarification.

Apr 9, 2010 12:36am

There appears to be some confusion in this post. There are E
There appears to be some confusion in this post. There are ELISA based VWF:RCo assays published in the literature, but none have been commercialized or incorporated into diagnostic practice. The IL assay is not a VWF:RCo assay – ristocetin is not used in this assay. Accordingly, the IL assay cannot replace the VWF:RCo assay. The IL assay is marketed as an activity assay, but this assay does not measure any VWF activity. The assay uses a monoclonal antibody coated onto latex beads to capture VWF and shows some preferential binding to high molecular weight VWF, and thus shows some correlation to VWF:RCo and other ‘activity’ assays such as collagen binding (VWF:CB). All VWF ‘activity’ assays have their limitations, including the IL latex assay, the VWF:RCo, and the VWF:CB. None can completely replace the other since each detects VWF differently. If you test 1000 cases including normals and patients with VWD with all assays for VWF, a correlation analysis will show a good regression line for any comparison, but there will be some cases, as few as 50 or so, which will not sit on the regression line. It is important to recognize that these 50 or so cases will be those that would be most interesting for further investigation. In the end, the best approach to VWD investigation is to perform as large a test panel as possible, incorporating more than one ‘activity’ assay, and to repeat testing for confirmation using a fresh collection, particularly when test findings are at odds withe the clinical evidence.

Leave a Reply