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Test ID: RIAS    
Ristocetin Inhibitor Assay Screen, Plasma

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosis of inhibitors of von Willebrand factor in patients with severe (type 3) von Willebrand disease (VWD)


Diagnosis of certain acquired types of VWD

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Inhibitors of the von Willebrand factor (VWF) may occur in those patients with severe type 3 von Willebrand's disease (VWD) who have a deletion of a large part of the von Willebrand gene.


Inhibitors may also occur in patients who have no previous evidence of VWD resulting in the development of a form of acquired VWD. Only a few of the patients with acquired VWD have evidence of an inhibitor. Most patients with acquired VWD have some type of B-cell lymphocytic abnormality (hairy cell leukemia, chronic lymphocytic leukemia, non-Hodgkin's lymphoma, multiple myeloma, monoclonal gammopathy of undetermined significance, Waldenstrom's macroglobulinemia, and systemic lupus erythematosus). Other patients with acquired VWD may have some form of myeloproliferative disease. Acquired VWD rarely arises in a person who is otherwise healthy.


Most inhibitors of VWF are IgG, but occasionally IgM and IgA have been reported.


Inhibiting antibodies to VWF are measured by determining the degree of inhibition of ristocetin/VWF-induced agglutination of washed normal platelets.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

An interpretive report will be provided.

Interpretation Provides information to assist in interpretation of the test results

An interpretive report is issued. Inhibitors may also occur in patients with severe type 3 von Willebrand disease. Unlike the acquired form of the disease, these latter patients will have a history of lifelong recurrent bleeding.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

The absence of an inhibitor does not exclude the diagnosis of acquired von Willebrand disease. In many patients, no inhibitor is demonstrable, but some of these patients may actually have an antibody which forms antigen-antibody complexes which are rapidly removed in the circulation.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. Gralnick HR: von Willebrand's disease. In Disorders of Hemostasis. Second edition. Edited by OD Ratnoff, CD Forbes. Philadelphia, WB Saunders Company, 1991, pp 203-244

2. Shapiro SS, Siegel JE: Hemorrhagic disorders associated with circulating inhibitors. In Disorders of Hemostasis. Second edition. Edited by OD Ratnoff, CD Forbes. Philadelphia, WB Saunders Company, 1991, pp 245-266

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test