2B or not 2B? Masquerading as von Willebrand disease?

Abstract

region associated with mild hemophilia A and resistance to DDAVP therapy. J Thromb Haemost 2009; 7: 1234-5. 13 Dai L, Cutler JA, Savidge GF, Mitchell MJ. Characterization of a causative mutation of hemophilia A identified in the promoter region of the factor VIII gene (F8 , this being the value most laboratories report using in surveys of practise [3,4], and also reflecting the current approved CLSI guideline [5]. However, it is recognized that some forms of 2B VWD, evidenced by mutational studies, may not show evidence of enhanced RIPA [2], or may only show RIPA at higher concentrations, as recently reported in a large study by Federici and colleagues [6], and as discussed in an accompanying commentary [7]. Notably, several 2B VWD patients failed to show a positive RIPA finding at 0.5 mg mL . The normal reference range for RIPA in this study was 0.8-1.2 mg mL . Indeed, RIPA is known to be poorly reproducible and not consistently reflective of VWD severity in other types of VWD [2]. Nevertheless, Ôlow-doseÕ RIPA responsiveness remains a diagnostic feature of 2B VWD (as well as its close cousin, platelet type VWD [9]), and the study by Federici and colleagues has led our laboratory (and presumably others) to re-evaluate Ôlow-doseÕ RIPA testing in this setting, essentially by extending the range of ristocetin concentrations used during the RIPA evaluation during our routine platelet function testing procedure.For these investigations, we initially assess responsiveness using 1.0 mg mL )1 and, for patients showing a response, sequentially test using lower concentrations, now including both 0.5 and 0.7mg mL, reflecting our classical 2B VWD cut-off and that identified by the Federici study [6]. It should be noted that our laboratory is very selective in terms of undertaking comprehensive platelet function studies, considering the highly time-consuming and technical nature of testing [10]. Accordingly this service is only offered to internal (hematology) newly referred patients with a significant history of bleeding or those with a previously diagnosed bleeding disorder for confirmation or exclusion, or for differential diagnosis of type 2 VWD and/or PT-VWD. Platelet function screening using the platelet function analyser-100 (PFA-100[11] is otherwise offered for clinicians requesting Ôplatelet function testingÕ for other indications.Of relevance to the current report is our recent observation of ÔenhancedÕ RIPA responsiveness in three out of 18 of our most recent platelet function evaluations using a RIPA cut-off value above 0.5 mg ristocetin mL )1. Thus, although these 18 patients reflected a variety of clinical histories and indications, two showed a significant aggregation response to ristocetin at 0.7 mg ristocetin mL )1, and one at 0.6 mg mL , but none at 0.5 mg mL )1 (Table 1). However, clinical histories and other laboratory studies were generally not suggestive of either 2B or PT VWD, most likely indicating these to be Ôfalse positivesÕ

2B or not 2B? A prothrombotic tendency masquerading as a bleeding disorder

“…Indeed, we recall seeing such a low level “false‐positive” (0.5 mg/mL) LD‐RIPA on only one other occasion in our experience, with this not being observed on repeat testing (i.e., was not reproducible) in that patient. However, ‘false positive’ events with responsiveness seen at 0.7, or less often at 0.6, mg/mL have occasionally been seen by us (as previously reported) . Alternatively, some patients with 2B‐VWD may not show evidence of enhanced RIPA or may only show RIPA positivity at concentrations higher than 0.5 mg/mL .…”

“…Although RIPA hyperresponsiveness is a defining feature of 2B or PT‐VWD, samples will infrequently provide false positive results, as in our patient, or false negative results. RIPA is practically challenging to perform, requiring rapid testing of freshly collected blood, and establishment of local normal and “pathological” ranges, with potentially frequent changes in ristocetin batches .…”

Identification of p.W246L As a Novel Mutation in the GP1BA Gene Responsible for Platelet-Type von Willebrand Disease

“…17 The cutoff values of ristocetin concentration in RIPA can contribute to false-negative or false-positive results. 55 On the basis of our experience, it is necessary to perform the assay with decreasing ristocetin concentrations, until reaching the lowest concentration that causes aggregation. This may vary between patients, especially according to the VWF:RCo levels.…”

Platelet-Type von Willebrand Disease: Toward an Improved Understanding of the “Sticky Situation”

“…The clinical diagnosis challenge stems from the close similarity of PT-VWD to the more common bleeding disorder, type 2B VWD. 2,3 The discrimination and correct diagnosis can only be made after carefully assessing less commonly performed laboratory tests, [3][4][5][6][7][8] and confirmed only after DNA analysis of the binding regions in the two genes VWF and GP1BA 9 has been performed.…”