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Von Willebrand Disease (VWD)
Part 2: NHLBI Diagnosis Guidelines

Laboratory Recommendations



Additional VWD Testing — Laboratory1

Slide 9

May 2011

This slide amplifies information from the preceding slide, concerning additional VWD specialized testing. Repeating the “VWD Panel” (the initial 3 VWD tests) is often indicated if initial VWD test results are abnormal, and is preferably done in the absence of patient conditions that can elevate VWF levels, and with careful attention to optimizing blood sample collection and processing (subsequent slides 20 to 22 have a summary of these patient and sample conditions). Evaluating the ratio of VWF ristocetin cofactor to VWF antigen is important for trying to differentiate between types 1 vs. types 2A, 2B or 2M VWD, or for recognizing the possibility of acquired von Willebrand syndrome or acquired von Willebrand abnormality if the ratio is discordant. However, the normal VWF cofactor to antigen ratio is not uniformly defined, depends on laboratory validation, is not available at all laboratories, and may vary significantly between laboratories (eg, ratios of 0.5 to 0.7). VWF multimer analysis is a complex qualitative assay that is frequently performed for additional specialized VWD testing to evaluate either low initial VWD test results, or an abnormal VWF ristocetin cofactor to VWF antigen ratio, and to help distinguish between type 1 VWD vs. types 2A, 2B or 2M VWD, as well as to detect some cases of acquired von Willebrand syndrome or acquired von Willebrand abnormality not identified by initial VWD testing. VWF multimer analysis is discussed in more detail in the next 3 slides. Ristocetin-induced platelet aggregometry (RIPA), using low dose ristocetin and the patient’s freshly prepared platelet-rich plasma (PRP), is primarily performed to evaluate for or exclude type 2B VWD (or “platelet-type” VWD, a rare variant) in which thrombocytopenia is often but not always present. But, this testing may require referring the patient to a specialized laboratory. Alternatively, a “VWF platelet-binding assay” may be available from selected reference laboratories and can be performed using patient plasma (sent frozen), but does not require patient PRP. VWF collagen binding activity (VWF:CB) is an alternative or supplemental measurement of VWF function, but is not widely available nor well standardized. The above are grade B recommendations, as is the FVIII-VWF binding assay that is used to evaluate for type 2N VWD.

Additional VWD Testing — Laboratory1

 


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