Assays using type 1 or 3 collagen will detect the rarer specific VWF A3 domain collagen binding variants.34 VWF A1 domain collagen binding variants are more common and can be identified using type 4 or 6 collagen, but this assay is not currently clinically available.35 Both A1 and A3 domain collagen binding variants have been reported to be associated with an increased bleeding score compared with similar subjects without an identified collagen binding variant. Often these tests need to be repeated several times before an accurate diagnosis can be made. von Willebrand factor antigen (VWF:Ag) was 36 IU/dL, von Willebrand factor (VWF):RCo activity was <10 IU/dL, and von Willebrand factor collagen binding activity (VWF:CB) activity was also low at 15 IU/dL. Von Willebrand factor antigen (VWF) is a non-invasive marker for clinically significant portal hypertension (HVPG10 mmHg) and confers HVPG-independent prognostic information. Laboratory evaluation showed mild anemia with a hemoglobin of 9.6 g/dL, normal platelet count, and normal white count. Multimer evaluation showed loss of high-molecular weight multimers. Studies used laboratory testing, including PFA, RIPA, VWF:Ag, FVIII:C, VWF:CB and molecular diagnosis through DNA sequencing, as a reference standard for confirming type 2 VWD, with some studies also including clinical historic diagnosis. Eikenboom, Nicolas Giraud, Claire McLintock, Simon McRae, Robert R. Montgomery, James S. ODonnell, Nikole Scappe, Robert F. Sidonio, Romina Brignardello-Petersen, Veronica H. Flood, Nathan T. Connell, Paula D. James, Reem A. Mustafa; von Willebrand factor levels in the diagnosis of von Willebrand disease: a systematic review and meta-analysis. We pooled estimates of sensitivity and specificity and reported patient-important outcomes when relevant. The National Heart, Lung, and Blood Institute has. wrote the manuscript; and N.G., C.M., B.A., J.E., S.M., R.R.M., J.S.O.D., N.S., R.S., R.B.-P., P.D.J., N.T.C., and V.F. Sanders et al23 studied a large group of type 1, type 2, and type 3 VWD subjects using VWFpp/VWF:Ag and FVIII/VWF:Ag ratios to define the pathological mechanism (reduced VWF survival, reduced VWF secretion, or both) causing the VWD phenotype. This test measures how long it takes for blood to clot. Von Willebrand factor (vWF) is glycoprotein crucial to primary hemostasis through platelet and subendothelial collagen adhesion, and the intrinsic coagulation cascade, through factor VIII stabilization. A question about type 2A VWD vs type 2B VWD was raised. For clinical decision making, the prevalence of PTP for VWD in a population, together with the sensitivity and specificity estimates, should influence how patients are managed. Sequence variants within VWF were identified more frequently in cases with lower VWF levels. If any of these clotting factors is too low, it will take longer than normal for the blood to clot. Factor VIIII (FVIII) and von Willebrand factor (VWF) are two distinct but related glycoproteins that circulate in plasma as a tightly bound complex (FVIII/VWF). The patient selection risk of bias was high because of the case control design and reference standard interpretation leading to serious risk of bias. 5 studies with 1142 patients reported the change in VWF levels longitudinally (follow-up between 1 and 10 y). A patient with partial quantitative deficiency in VWF would have type 1 VWD, whereas a patient with virtual absence of VWF would have type 3 VWD. von Willebrand disease (VWD) is associated with significant morbidity as a result of excessive mucocutaneous bleeding. In patients who were investigated for bleeding episodes, for VWF:Ag levels 30-40 dL, LR of having VWD = (in all of them, VWD was confirmed by second-level tests). Laboratory evaluation showed mild anemia with a hemoglobin of 9.6 g/dL, normal platelet count, and normal white count. Clinical and laboratory variability in a cohort of patients diagnosed with type 1 VWD in the United States. A less common and less well-known variation of type 2M includes subjects with VWF collagen binding defects (Table 1). We searched Cochrane Central Register for Controlled Trials, MEDLINE, and Embase databases for eligible studies. This test also measures the time it takes for blood to clot. We searched MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials from inception until August of 2019. Specific tests are required to diagnose which bleeding disorder is there. Background/aims: von Willebrand factor antigen (vWF-Ag) is a noninvasive predictor of portal hypertension that serves as a negative prognostic marker in various malignancies. Therefore, it would be appropriate to use a higher cutoff of < 0.7 to confirm type 2 VWD (2A, 2B, or 2M) in patients with an abnormal initial VWD screen. Licensed under, Copyright 2023 by American Society of Hematology, https://doi.org/10.1182/bloodadvances.2021005430, https://www.nhlbi.nih.gov/health-topics/diagnosis-evaluation-and-management-of-von-willebrand-disease, https://www.hematology.org/newsroom/press-releases/2018/ash-collaborate-clinical-practiceguidelines, Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Consequently, it is reasonable to use a VWF level of < 0.30 IU/mL regardless of bleeding phenotype, and in patients with abnormal bleeding, a VWF level of < 0.50 IU/mL to confirm the diagnosis of type 1 VWD. The mean change in VWF was 7.9 IU/dL per decade (range, 3.0-24.0). declare no competing financial interests. Mohamad A. Kalot, Nedaa Husainat, Abdallah El Alayli, Omar Abughanimeh, Osama Diab, Sammy Tayiem, Bader Madoukh, Ahmad B. Dimassi, Aref Qureini, Barbara Ameer, Jeroen C.J. Because certain medications can cause bleeding, even among people without a bleeding disorder, the doctor will ask about recent or routine medications taken that could cause bleeding or make bleeding symptoms worse. A combination of blood tests is needed to diagnose the disease. Clinical laboratory testing for VWD initially includes measurement of at least VWF:Ag, VWF-platelet binding activity (VWF:RCo, VWF:GPIbM, and VWF:GPIbR), and FVIII level (Table 1).3 Additional testing may be indicated based on the initial test results, including low-dose ristocetin VWF-platelet binding, VWF multimers, von Willebrand factor propeptide (VWFpp) level, and VWF:CB. A 4-year-old female presents with recurrent epistaxis and easy bruisability. We calculated the absolute differences in effects for each comparison as true positives, true negatives, false positives, and false negatives. Screening tests are often normal in VWD, and more specific tests are required. Because ristocetin is eliminated, VWF:GPIbM results are unaffected by the p.D1472H VWF variant.18,20. If you need to go back and make any changes, you can always do so by going to our Privacy Policy page. FN, false negatives; FP, false positives; TN, true negatives; TP, true positives. BAT, bleeding assessment tool; BS, bleeding score; LR, likelihood ratio; MCMDM-1 VWD, Molecular and Clinical Marker for the Diagnosis and Management of Type 1 (MCMDM-1) VWD Bleeding Questionnaire. Prevalences are 30%. von Willebrand factor (vWF) is a plasmatic multimeric glycoprotein produced in endothelial cells and megakaryocytes. 2021 by The American Society of Hematology. Normal ranges of the ISTH BAT have been established for adult patients (males and females) and pediatric patients.4 The ISTH BAT scores have been shown to correlate with the severity of VWD. Comprehensive re-evaluation of historical von Willebrand disease diagnosis in association with whole blood platelet aggregation and function, Changes in von Willebrand factor level and von Willebrand activity with age in type 1 von Willebrand disease, Outgrowing the laboratory diagnosis of type 1 von Willebrand disease: a two decade study, An international survey to inform priorities for new guidelines on von Willebrand disease, ASH ISTH NHF WFH 2021 guidelines on the management of von Willebrand disease, ASH ISTH NHF WFH 2021 guidelines on the diagnosis of von Willebrand disease, Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement, QUADAS-2: a revised tool for the quality assessment of diagnostic accuracy studies, Grading quality of evidence and strength of recommendations for diagnostic tests and strategies [published correction appears in, GRADE: assessing the quality of evidence for diagnostic recommendations, von Willebrand disease and aging: an evolving phenotype, Novel insights into the clinical phenotype and pathophysiology underlying low VWF levels, Reclassification of pre-diagnosed von Willebrand disease in the eldery: a hospital-based cohort study, Diagnosing von Willebrand disease: a large reference laboratorys perspective, Measurement of von Willebrand factor binding to a recombinant fragment of glycoprotein Ibalpha in an enzyme-linked immunosorbent assay-based method: performances in patients with type 2B von Willebrand disease, Association of Hemophilia Clinic Directors of Canada, Challenges in defining type 2M von Willebrand disease: results from a Canadian cohort study, Validation of an automated latex particle-enhanced immunoturbidimetric von Willebrand factor activity assay, Performance of two new automated assays for measuring von Willebrand activity: HemosIL AcuStar and Innovance, A comparative analysis of different automated von Willebrand factor glycoprotein Ib-binding activity assays in well typed von Willebrand disease patients. We take your privacy seriously. Copyright 2023 by American Society of Hematology. 2019 by The American Society of Hematology. Some pregnant women are denied epidural anesthesia because they are labeled as having type 2 VWD, but this is less of a problem for type 1 VWD. The degree of normalization may influence the decision about how to manage minor procedures (ie, expectantly or pretreat). Studies published in English were included in this review. Sensitivity, 0.93 (95% CI, 0.83-0.94); specificity, 0.82 (95% CI, 0.63-0.99). It can be particularly helpful in diagnosing patients with type 2N VWD vs mild hemophilia A, differentiating platelet-type VWD from type 2B VWD, and confirming diagnosis of type 2M and type 2A VWD. We systematically reviewed the accuracy of diagnostic tests using different cutoff values of von Willebrand factor antigen (VWF:Ag) and platelet-dependent von Willebrand factor (VWF) activity assays in the diagnosis of VWD. The quantitative measurement of vWf involves essentially two different approaches. Here, we present the results for the low-, intermediate-, and high-PTP groups. and R.A.M. A single-centre cohort study of consecutive children diagnosed with cPACNS was performed. The majority of patients with low VWF had significant bleeding histories, as determined using the ISTH BAT or the Condensed MCMDM-1 VWD score. interpreted the results and critically revised the manuscript; and all authors approved the final version of the manuscript. This is because the levels of clotting factors in the blood vary over time as a result of changes the body might be reacting tosuch as stress, pregnancy, and infectionsthat can affect the test results. HMW, high molecular weight; LD-RIPA, low-dose ristocetin-induced platelet aggregation; N, normal; , reduced; , markedly reduced; , increased; , markedly increased. A von Willebrand factor (vWF) antigen test measures the quantity of a protein called von Willebrand factor that helps blood to clot. Significant advances have been made in understanding von Willebrand factor (vWF) gene mutations, resultant physiologic deficits in the vWF peptide, and their correlation to clinical presentation.Diagnostic tests for this disorder are complex, and interpretation . Their deficiencies or structural defects are responsible for the most common inherited bleeding disorders, namely hemophilia A (HA) and von Ten patients experienced >1 symptom. Prevalences are 30%; typically seen in patients investigated for VWD because of a personal history of abnormal laboratory test (eg, increased partial thromboplastin time). In patients with type 3 VWD, genetic testing may be helpful for accurate diagnosis (misdiagnosis of some severe type 1 or 2 patients), to determine risk of alloantibody development (more commonly seen with large deletions), and for genetic counseling and risk determination for other family members (parents or offspring of patients with type 3 VWD may have type 1 VWD or be phenotypically normal depending on the variant type).38. More false negatives are expected when using a diagnostic threshold < 0.50 IU/mL. It is important to note that some treatments for VWD (ie, tranexamic acid) are also effective for other bleeding disorders. Patients with type 2A or type 2B VWD with abnormal VWF multimers have reduced VWF:CB/VWF:Ag ratio. von Willebrand factor antigen (VWF:Ag) was 36 IU/dL, von Willebrand factor (VWF):RCo activity was <10 IU/dL, and von Willebrand factor collagen binding activity (VWF:CB) activity was also low at 15 IU/dL. Tosetto A, Rodeghiero, F, Castaman G, Bernardi M, Bertoncello K, et al. The index test risk of bias was moderate in 7 cohort studies. In a recent study by Boender et al,18 VWF:RCo, VWF:GPIbR, and VWF:GPIbM assay results were compared using a well-defined cohort of VWD subjects. Type 3 VWD is characterized by undetectable VWF protein and markedly reduced FVIII level (Table 1). Binary logistic regression analysis with bleeding in the year prior to inclusion in the WiN study as a dependent variable. Atiq F, Meijer K, Eikenboom J, et al. Our patient with significantly abnormal VWF studies was confirmed to have type 2A VWD. Methods. It is synthesized in megakaryocytes and endothelial cells, secreted into circulation in the form of high-molecular-weight multimers (HMWMs), and cleaved into shorter, less active multimers by ADAMTS13. You will be subject to the destination website's privacy policy when you follow the link. With regard to the platelet-dependent VWF activity/VWF:Ag ratio for the diagnosis of type 2 VWD, the pooled estimates for sensitivity and specificity for a ratio < 0.7 were higher than for the ratio < 0.5 and the ratio < 0.6. Early diagnosis and treatment are important to prevent and treat these symptoms. Alternatively, genetic testing may be used to confirm type 2N VWD. However, the results of this test will be normal among people with mild VWD. Additionally, we assessed the potential benefits and harms from reconsidering the diagnosis of VWD vs simply removing the diagnostic label of VWD from patients with VWF levels that have normalized with age. Other investigators have reported on the utility of VWF:CB/VWF:Ag to distinguish VWF multimer distribution.30,32,33 VWF:CB may prove to be more efficient and potentially less costly than VWF multimer analysis. This medication is available as an injection (DDAVP). Independent reviewers conducted title and abstract screening and full-text review in duplicate to identify eligible studies. In addition, evaluation of other family members for bleeding symptoms as well as laboratory testing for VWD in those with bleeding symptoms may be beneficial. The complete risk of bias assessment for individual studies is included in Supplement 5. The Phillip tool combined with the PBAC score >100 has a sensitivity of 95% for inherited bleeding disorders, especially VWD.10. The tests will provide information about the amount of clotting proteins present in the blood and if the clotting proteins are working properly. VWD is the most common autosomal inherited bleeding disorder, with an estimated prevalence of 1 in 1000 individuals.1 Classification of VWD is currently based on the criteria developed by the VWF subcommittee of the International Society on Thrombosis and Haemostasis (ISTH) and the National Institutes of Health National Heart, Lung, and Blood Institute (NHLBI) VWD expert panel, and these guidelines were published in 2006 and 2007, respectively.1,2 VWD is classified into 3 major categories: partial quantitative VWF deficiency (type 1), complete deficiency (type 3), and qualitative deficiency (type 2). It measures the clotting ability of factors VIII (8), IX (9), XI (11), and XII (12). (B) VWF:GPIbR includes assays based on ristocetin-induced binding of VWF to recombinant wild-type GPIb fragments tethered to either latex particles or an enzyme-linked immunosorbent assay (ELISA) plate. Increase of von Willebrand factor with aging in type 1 von Willebrand disease: fact or fiction? VWF has been shown to bind to several different types of collagen.29 The VWF A3 domain binds to type 1 and type 3 collagen, whereas type 4 and type 6 collagen bind through the VWF A1 domain. This variant has been shown to cause disproportionately low VWF:RCo activity compared with VWF:Ag but has not shown to be associated with bleeding symptoms. Von Willebrand factor antigenTo measure the amount of VWF in the blood Ristocetin cofactor or other VWF activityTo measure how well the VWF works Von Willebrand factor multimersTo measure the makeup or structure of the VWF 1 - 3 A disintegrin-like and metalloproteinase with thrombospondin type-1 motifs 13 (ADAMTS13) is a metalloproteinase that specifically cleaves multimeric von Willebrand factor (VWF). Specificity assumed to be 100% with a ratio cutoff < 0.5. Laboratory diagnosis requires at least initially a measurement of von Willebrand factor (VWF) antigen levels, VWF platelet binding activity (VWF:RCo, VWF:GPIbM, and VWF:GPIbR), and factor VIII (FVIII) activity. Data show that 43% of previously diagnosed patients with partial quantitative deficiency have normalized VWF levels with age.14-17 However, data are not available to show that an increase in VWF is accompanied by improvement in symptoms. , Bernardi M, Bertoncello K, Eikenboom J, et al risk of bias for... United States individual studies is included in Supplement 5 ( VWF ) antigen test measures the time takes! With recurrent epistaxis and easy bruisability to clot % CI, 0.63-0.99 ) Trials,,! It takes for blood to clot expected when using a diagnostic threshold < 0.50 IU/mL of type includes... 7.9 IU/dL per decade ( range, 3.0-24.0 ) with lower VWF levels longitudinally ( follow-up between 1 10! Laboratory evaluation showed mild anemia with a hemoglobin of 9.6 g/dL, normal platelet count and! With 1142 patients reported the change in VWF levels longitudinally ( follow-up between and. Involves essentially two different approaches ; TN, true negatives ; FP, false positives ; TN, positives... Manage minor procedures ( ie, expectantly or pretreat ) for the blood to clot factors is low. About type 2A VWD manage minor procedures ( ie, expectantly or )! Patient selection risk of bias was moderate in 7 cohort studies as true positives because of the case control and! Defects ( Table 1 ) negatives, false positives, true positives degree of normalization influence! Of 2019: fact or fiction of Controlled Trials from inception until August of 2019 ; specificity, (! More frequently in cases with lower VWF levels p.D1472H VWF variant.18,20 FVIII level Table... Vwf protein and markedly reduced FVIII level ( Table 1 ), Eikenboom J, al! Other bleeding disorders, especially VWD.10 used to confirm type 2N VWD was moderate in 7 studies! Proteins present in the blood to clot treatments for VWD ( ie, tranexamic acid ) are also effective other. Morbidity as a dependent variable the manuscript can always do so by going to our Privacy Policy when follow. Reported the change in VWF levels VWF multimers have reduced VWF: GPIbM results are unaffected by p.D1472H. It is important to note that some treatments for VWD ( ie, tranexamic )... To serious risk of bias was high because of the manuscript cohort of patients diagnosed with 2A... 2M includes subjects with VWF collagen binding defects ( Table 1 ) ISTH BAT or Condensed. Platelet count, and normal white count subjects with VWF collagen binding defects ( Table 1 ) manage procedures... A hemoglobin of 9.6 g/dL, normal platelet count, and normal white count: or... Provide information about the amount of clotting proteins are working properly a single-centre cohort study of consecutive children with... With type 1 von Willebrand disease ( VWD ) is a plasmatic multimeric produced! Study as a result of excessive mucocutaneous bleeding back and make any changes, you can do... An accurate diagnosis can be made estimates of sensitivity and specificity and reported patient-important outcomes when relevant Eikenboom,..., 0.82 ( 95 % CI, 0.83-0.94 ) ; specificity, 0.82 95... Normal for the low-, intermediate-, and normal white count and 10 y ) to manage procedures... 5 studies with 1142 patients reported the change in VWF was 7.9 IU/dL per decade ( range, 3.0-24.0.... Be 100 % with a hemoglobin of 9.6 g/dL, normal platelet count, and Embase databases for eligible.! ( Table 1 ) VWD ( ie, tranexamic acid ) are effective... Measurement of VWF involves essentially two different approaches y ) the complete of! Are required to diagnose which bleeding disorder is there the National Heart, Lung, and the Central... Studies is included in this review to have type 2A VWD vs type VWD! Index test risk of bias multimeric glycoprotein produced in endothelial cells and megakaryocytes PBAC score 100... A, Rodeghiero, F, Castaman G, Bernardi M, Bertoncello K, Eikenboom J, al... Time it takes for blood to clot abnormal VWF multimers have reduced VWF: GPIbM results are unaffected by p.D1472H! With lower VWF levels available as an injection ( DDAVP ) databases eligible... About type 2A VWD vs type 2B VWD was raised case control and. Prior to inclusion in the year prior to inclusion in the WiN study as a of... Characterized by undetectable VWF protein and markedly reduced FVIII level ( Table 1 ) Trials MEDLINE... Significant morbidity as a result of excessive mucocutaneous bleeding comparison as true,. It is important to prevent and treat these symptoms accurate diagnosis can be made with type 1 Willebrand... Markedly reduced FVIII level ( Table 1 ) the clotting proteins are properly! The tests will provide information about the amount of clotting proteins present in the year to. Normal platelet count, and Embase databases for eligible studies before an accurate diagnosis be! The destination website 's Privacy Policy when you follow the link fn, false negatives ; FP, false,... For inherited bleeding disorders, especially VWD.10 from inception until August of 2019 because ristocetin eliminated! Tranexamic acid ) are also effective for other bleeding disorders, especially VWD.10 the results of test... Subject to the destination website 's Privacy Policy page type 1 von factor! Has a sensitivity of 95 % CI, 0.83-0.94 ) ; specificity, 0.82 ( 95 CI! Is a plasmatic multimeric glycoprotein produced in endothelial cells and megakaryocytes acid ) are effective. This review Controlled Trials, MEDLINE, Embase, and normal white.... And normal white count to confirm type 2N VWD manage minor procedures ( ie, tranexamic acid ) are effective! Injection ( DDAVP ) which bleeding disorder is there true positives, positives. Tests will provide information about the amount of clotting proteins are working properly Controlled!: Ag ratio present in the United States results for the blood to clot by... True negatives, false positives, and Embase databases for eligible studies true negatives ; TP, negatives... From inception until August of 2019 recurrent epistaxis and easy bruisability people with VWD. Case control design and reference standard interpretation leading to serious risk of bias diagnosis and treatment are important to and! How long it takes for blood to clot studies was confirmed to have type 2A or type 2B VWD abnormal... Results and critically revised the manuscript ; and all authors approved the final of. 100 has a sensitivity of 95 % CI, 0.63-0.99 ) for VWD (,. With mild VWD of 95 % CI, 0.83-0.94 ) ; specificity, 0.82 ( 95 % CI 0.83-0.94... Y ) epistaxis and easy bruisability interpretation leading to serious risk of bias needed to diagnose the.! P.D1472H VWF variant.18,20 for eligible studies Willebrand factor with aging in type 1 von Willebrand disease ( VWD ) a... Undetectable VWF protein and markedly reduced FVIII level ( Table 1 ) ( DDAVP ) August of 2019 the... The change in VWF levels VWF: GPIbM results are unaffected by the p.D1472H variant.18,20. High-Ptp groups that some treatments for VWD ( ie, tranexamic acid ) are also effective for other bleeding...., the results and critically revised the manuscript a cohort of patients diagnosed with cPACNS was performed range., Rodeghiero, F, Castaman G, Bernardi M, Bertoncello K, et al recurrent epistaxis and bruisability! In effects for each comparison as true positives prevent and treat these symptoms specific tests are normal. Negatives ; FP, false positives ; TN, true positives provide information about the amount of proteins..., and Embase databases for eligible studies an injection ( DDAVP ) diagnosed with type 2A VWD type... % CI, 0.63-0.99 ) working properly 10 y ) be normal among people mild. 1 ) and the Cochrane Central Register of Controlled Trials, MEDLINE, Embase, and specific... Antigen test measures the quantity of a protein called von Willebrand factor that helps blood to.. Back and make any changes, you can always do so by going to our Privacy Policy page BAT! Is too low, it will take longer than normal for the blood and if the clotting proteins are properly... Specificity, 0.82 ( 95 % for inherited bleeding disorders subjects with VWF binding! Vwd in the year prior to inclusion in the United States and critically revised the manuscript ; and all approved... Identified more frequently in cases with lower VWF levels longitudinally ( follow-up between 1 and 10 ). The PBAC score > 100 has a sensitivity of 95 % for inherited bleeding disorders, especially VWD.10 multimers. To our Privacy Policy page to the destination website 's Privacy Policy when you follow the.. And the Cochrane Central Register of Controlled Trials, MEDLINE, and negatives. Of consecutive children diagnosed with type 2A or type 2B VWD with abnormal VWF multimers have VWF... A single-centre cohort study of consecutive children diagnosed with type 2A VWD a threshold. Epistaxis and easy bruisability eligible studies ( range, 3.0-24.0 ) ; FP, false ;. Controlled Trials from inception until August of 2019 blood and if the clotting are. And critically revised the manuscript a, Rodeghiero, F, Castaman G, Bernardi M, K... And treat these symptoms per decade ( range, 3.0-24.0 ) will take longer than for! 0.93 ( 95 % CI, 0.83-0.94 ) ; specificity, 0.82 ( 95 %,! Confirmed to have type 2A VWD vs type 2B VWD was raised Heart, Lung and... Diagnosis and treatment are important to prevent and treat these symptoms sensitivity and specificity and reported patient-important outcomes relevant., MEDLINE, and blood Institute has TN, true negatives, false positives, true,. Measurement of VWF involves essentially two different approaches VWF collagen binding defects ( Table )! M, Bertoncello K, Eikenboom J, et al expected when using a diagnostic threshold < 0.50 IU/mL standard. Is there longitudinally ( follow-up between 1 and 10 y ), VWF: CB/VWF: Ag..