Von Willebrand Factor (VWF) multiplex activity assay differentiation of type 1 von Willebrand Disease (VWD) and variant VWD.

INTRODUCTION: VWD diagnosis is challenging requiring multiple VWF activity tests using many individual assays. We have developed an ELISA-based VWF Multiplex Activity Assay (VWF-MAA) to address this concern; however, the ability of the VWF-MAA to discriminate between type 1 VWD, variant VWD, and normal subjects has not been evaluated. AIM: To evaluate the VWF-MAA and its ability to differentiate between type 1 VWD, variant VWD and normal subjects in individuals undergoing an initial laboratory evaluation for bleeding. METHODS: A total of 177 plasma samples from the Zimmerman Program: Comparative Effectiveness in the Diagnosis of VWD were evaluated from 11 centres across the US and Canada. The VWF-MAA was compared to Versiti Blood Research Institute (VBRI) and Local Center (LC) assigned VWD diagnosis. RESULTS: Overall, 129/177 (72.9%) were correctly assigned as normal (non-VWD), type 1, or variant VWD compared to the VBRI assigned diagnosis. VWF-MAA assigned non-VWD accurately in 29/57 (50.9%) samples, and type 1 VWD accurately in 93/110 (84.6%) samples. Considering LC diagnosis where there was agreement with VWF-MAA and not VBRI diagnosis, type 1 VWD was accurate in 105/110 (95.5%) samples. Bland-Altman analysis demonstrated good correlation between laboratory methods. VWD, types 2A, 2B, 1C VWD were also assigned by the VWF-MAA. CONCLUSIONS: We demonstrate that the VWF-MAA has utility in differentiating type 1 VWD, variant VWD and normal subjects in individuals undergoing an initial laboratory evaluation for bleeding.

Effect of Anticoagulant Therapy for 6 Weeks vs 3 Months on Recurrence and Bleeding Events in Patients Younger Than 21 Years of Age With Provoked Venous Thromboembolism: The Kids-DOTT Randomized Clinical Trial.

Importance: Among patients younger than 21 years of age, the optimal duration of anticoagulant therapy for venous thromboembolism is unknown. Objective: To test the hypothesis that a 6-week duration of anticoagulant therapy for provoked venous thromboembolism is noninferior to a conventional 3-month therapy duration in patients younger than 21 years of age. Design, Setting, and Participants: Randomized clinical trial involving 417 patients younger than 21 years of age with acute, provoked venous thromboembolism enrolled at 42 centers in 5 countries from 2008-2021. The main exclusions were severe anticoagulant deficiencies or prior venous thromboembolism. Patients without persistent antiphospholipid antibodies and whose thrombi were resolved or not completely occlusive upon repeat imaging at 6 weeks after diagnosis underwent randomization. The final visit for the primary end points occurred in January 2021. Interventions: Total duration for anticoagulant therapy of 6 weeks (n = 207) vs 3 months (n = 210) for provoked venous thromboembolism. Main Outcomes and Measures: The primary efficacy and safety end points were centrally adjudicated symptomatic recurrent venous thromboembolism and clinically relevant bleeding events within 1 year blinded to treatment group. The primary analysis was noninferiority in the per-protocol population. The noninferiority boundary incorporated a bivariate trade-off that included an absolute increase of 0% in symptomatic recurrent venous thromboembolism with an absolute risk reduction of 4% in clinically relevant bleeding events (1 of 3 points on the bivariate noninferiority boundary curve). Results: Among 417 randomized patients, 297 (median age, 8.3 [range, 0.04-20.9] years; 49% female) met criteria for the primary per-protocol population analysis. The Kaplan-Meier estimate for the 1-year cumulative incidence of the primary efficacy outcome was 0.66% (95% CI, 0%-1.95%) in the 6-week anticoagulant therapy group and 0.70% (95% CI, 0%-2.07%) in the 3-month anticoagulant therapy group, and for the primary safety outcome, the incidence was 0.65% (95% CI, 0%-1.91%) and 0.70% (95% CI, 0%-2.06%). Based on absolute risk differences in recurrent venous thromboembolism and clinically relevant bleeding events between groups, noninferiority was demonstrated. Adverse events occurred in 26% of patients in the 6-week anticoagulant therapy group and in 32% of patients in the 3-month anticoagulant therapy group; the most common adverse event was fever (1.9% and 3.4%, respectively). Conclusions and Relevance: Among patients younger than 21 years of age with provoked venous thromboembolism, anticoagulant therapy for 6 weeks compared with 3 months met noninferiority criteria based on the trade-off between recurrent venous thromboembolism risk and bleeding risk. Trial Registration: ClinicalTrials.gov Identifier: NCT00687882.

Screening for von Willebrand disease does not impact posttonsillectomy bleeding in a low-risk population.

BACKGROUND: Bleeding is an important complication in children following tonsillectomy. Screening with coagulation tests prior to procedure is common to assess bleeding risk in the perioperative period, although ASH/ASPHO Choosing Wisely guidelines recommend against routine PT/PTT testing. Our aim was to compare von Willebrand factor antigen (VWF:Ag) and activity levels among patients with postoperative bleeding following tonsillectomy to evaluate for potential risk for bleeding. PROCEDURE: Eligible subjects were aged 0-18 without significant personal or family history of major bleeding. Postoperative bleeding diaries were collected and symptoms measured using a postoperative bleeding score. Plasma VWF levels were drawn at time of anesthesia administration. RESULTS: Postoperative bleeding occurred in 248 cases out of 1399 total subjects. Median VWF:Ag was 86 in patients with postoperative bleeding scores of 1-2, 86 for scores 3-4, 84 for scores 5-6, and 83 for scores >6, with no significant difference among groups (p = .98). Additionally, no difference was observed for subjects with multiple days of postoperative bleeding as compared to those with only 1 day of postoperative bleeding. Finally, no difference in VWF:Ag was observed for subjects whose first reported bleed occurred early in the postoperative course compared to those whose first reported bleed occurred later. VWF:Ag does not correlate with severity of bleeding, time of onset of first bleeding event, or recurrence of bleeding in healthy children with no personal or family history of bleeding who have postoperative bleeding following tonsillectomy. CONCLUSIONS: This data does not support routine von Willebrand disease screening prior to tonsillectomy.

Factor VIII prophylaxis effects outweigh other hemostasis contributors in predicting severe haemophilia A joint outcomes.

INTRODUCTION: The Joint Outcome Study (JOS) demonstrated that previously untreated children with severe haemophilia A treated with prophylactic factor VIII (FVIII) concentrate had superior joint outcomes at age 6 years compared to those children treated episodically for bleeding. However, variation in joint outcome within each treatment arm was not well explained. AIM: In this study, we sought to better understand variation in joint outcomes at age 6 years in participants of the JOS. METHODS: We evaluated the influence of FVIII half-life, treatment adherence, constitutional coagulant and anticoagulant proteins, and global assays on joint outcomes (number of joint bleeds, total number of bleeds, total MRI score and joint physical exam score). Logistic regression was used to evaluate the association of variables with joint failure status on MRI, defined as presence of subchondral cyst, surface erosion or joint-space narrowing. Each parameter was also correlated with each joint outcome using Spearman correlations. RESULTS: Prophylaxis treatment arm and FVIII trough were each found to reduce risk of joint failure on univariate logistic regression analysis. When controlling for treatment arm, FVIII trough was no longer significant, likely because of the high level of covariation between these variables. We found no consistent correlation between any laboratory assay performed and any joint outcome parameter measured. CONCLUSION: In the JOS, the effect of prescribed prophylactic FVIII infusions on joint outcome overshadowed the contribution of treatment adherence, FVIII half-life, global assays of coagulation and constitutional coagulation proteins. (ClinicalTrials.gov number, NCT00207597).

Clinical and laboratory variability in a cohort of patients diagnosed with type 1 VWD in the United States.

von Willebrand disease (VWD) is the most common inherited bleeding disorder, and type 1 VWD is the most common VWD variant. Despite its frequency, diagnosis of type 1 VWD remains the subject of debate. In order to study the spectrum of type 1 VWD in the United States, the Zimmerman Program enrolled 482 subjects with a previous diagnosis of type 1 VWD without stringent laboratory diagnostic criteria. von Willebrand factor (VWF) laboratory testing and full-length VWF gene sequencing was performed for all index cases and healthy control subjects in a central laboratory. Bleeding phenotype was characterized using the International Society on Thrombosis and Haemostasis bleeding assessment tool. At study entry, 64% of subjects had VWF antigen (VWF:Ag) or VWF ristocetin cofactor activity below the lower limit of normal, whereas 36% had normal VWF levels. VWF sequence variations were most frequent in subjects with VWF:Ag <30 IU/dL (82%), whereas subjects with type 1 VWD and VWF:Ag ≥30 IU/dL had an intermediate frequency of variants (44%). Subjects whose VWF testing was normal at study entry had a similar rate of sequence variations as the healthy controls (14%). All subjects with severe type 1 VWD and VWF:Ag ≤5 IU/dL had an abnormal bleeding score (BS), but otherwise BS did not correlate with VWF:Ag. Subjects with a historical diagnosis of type 1 VWD had similar rates of abnormal BS compared with subjects with low VWF levels at study entry. Type 1 VWD in the United States is highly variable, and bleeding symptoms are frequent in this population.

No increase in bleeding identified in type 1 VWD subjects with D1472H sequence variation.

The diagnosis of von Willebrand disease (VWD) is complicated by issues with current laboratory testing, particularly the ristocetin cofactor activity assay (VWF:RCo). We have recently reported a sequence variation in the von Willebrand factor (VWF) A1 domain, p.D1472H (D1472H), associated with a decrease in the VWF:RCo/VWF antigen (VWF:Ag) ratio but not associated with bleeding in healthy control subjects. This report expands the previous study to include subjects with symptoms leading to the diagnosis of type 1 VWD. Type 1 VWD subjects with D1472H had a significant decrease in the VWF:RCo/VWF:Ag ratio compared with those without D1472H, similar to the findings in the healthy control population. No increase in bleeding score was observed, however, for VWD subjects with D1472H compared with those without D1472H. These results suggest that the presence of the D1472H sequence variation is not associated with a significant increase in bleeding symptoms, even in type 1 VWD subjects.

VWF mutations and new sequence variations identified in healthy controls are more frequent in the African-American population.

Diagnosis and classification of VWD is aided by molecular analysis of the VWF gene. Because VWF polymorphisms have not been fully characterized, we performed VWF laboratory testing and gene sequencing of 184 healthy controls with a negative bleeding history. The controls included 66 (35.9%) African Americans (AAs). We identified 21 new sequence variations, 13 (62%) of which occurred exclusively in AAs and 2 (G967D, T2666M) that were found in 10%-15% of the AA samples, suggesting they are polymorphisms. We identified 14 sequence variations reported previously as VWF mutations, the majority of which were type 1 mutations. These controls had VWF Ag levels within the normal range, suggesting that these sequence variations might not always reduce plasma VWF levels. Eleven mutations were found in AAs, and the frequency of M740I, H817Q, and R2185Q was 15%-18%. Ten AA controls had the 2N mutation H817Q; 1 was homozygous. The average factor VIII level in this group was 99 IU/dL, suggesting that this variation may confer little or no clinical symptoms. This study emphasizes the importance of sequencing healthy controls to understand ethnic-specific sequence variations so that asymptomatic sequence variations are not misidentified as mutations in other ethnic or racial groups.

Inhibitors of factor VIII in black patients with hemophilia.

BACKGROUND: Black patients with hemophilia A (factor VIII deficiency) are twice as likely as white patients to produce inhibitors against factor VIII proteins given as replacement therapy. There are six wild-type factor VIII proteins, designated H1 through H6, but only two (H1 and H2) match the recombinant factor VIII products used clinically. H1 and H2 are found in all racial groups and are the only factor VIII proteins found in the white population to date. H3, H4, and H5 have been found only in blacks. We hypothesized that mismatched factor VIII transfusions contribute to the high incidence of inhibitors among black patients. METHODS: We sequenced the factor VIII gene (F8) in black patients with hemophilia A to identify causative mutations and the background haplotypes on which they reside. Results from previous Bethesda assays and information on the baseline severity of hemophilia, age at enrollment, and biologic relationships among study patients were obtained from review of the patients' medical charts. We used multivariable logistic regression to control for these potential confounders while testing for associations between F8 haplotype and the development of inhibitors. RESULTS: Of the 78 black patients with hemophilia enrolled, 24% had an H3 or H4 background haplotype. The prevalence of inhibitors was higher among patients with either of these haplotypes than among patients with haplotype H1 or H2 (odds ratio, 3.6; 95% confidence interval, 1.1 to 12.3; P=0.04), despite a similar spectrum of hemophilic mutations and degree of severity of illness in these two subgroups. CONCLUSIONS: These preliminary results suggest that mismatched factor VIII replacement therapy may be a risk factor for the development of anti-factor VIII alloantibodies.

Common VWF exon 28 polymorphisms in African Americans affecting the VWF activity assay by ristocetin cofactor.

The diagnosis of von Willebrand disease relies on abnormalities in specific tests of von Willebrand factor (VWF), including VWF antigen (VWF:Ag) and VWF ristocetin cofactor activity (VWF:RCo). When examining healthy controls enrolled in the T. S. Zimmerman Program for the Molecular and Clinical Biology of von Willebrand disease, we, like others, found a lower mean VWF:RCo compared with VWF:Ag in African American controls and therefore sought a genetic cause for these differences. For the African American controls, the presence of 3 exon 28 single nucleotide polymorphisms (SNPs), I1380V, N1435S, and D1472H, was associated with a significantly lower VWF:RCo/VWF:Ag ratio, whereas the presence of D1472H alone was associated with a decreased ratio in both African American and Caucasian controls. Multivariate analysis comparing race, SNP status, and VWF:RCo/VWF:Ag ratio confirmed that only the presence of D1472H was significant. No difference was seen in VWF binding to collagen, regardless of SNP status. Similarly, no difference in activity was seen using a GPIb complex-binding assay that is independent of ristocetin. Because the VWF:RCo assay depends on ristocetin binding to VWF, mutations (and polymorphisms) in VWF may affect the measurement of "VWF activity" by this assay and may not reflect a functional defect or true hemorrhagic risk.

Evaluating for Suspected Child Abuse: Conditions That Predispose to Bleeding.

Child abuse might be suspected when children present with cutaneous bruising, intracranial hemorrhage, or other manifestations of bleeding. In these cases, it is necessary to consider medical conditions that predispose to easy bleeding or bruising. When evaluating for the possibility of bleeding disorders and other conditions that predispose to hemorrhage, it is important for pediatricians to consider the child's presenting history, medical history, and physical examination findings before initiating a laboratory investigation. Many medical conditions can predispose to easy bleeding. Before ordering laboratory tests for a disease, it is useful to understand the biochemical basis and clinical presentation of the disorder, condition prevalence, and test characteristics. This technical report reviews the major medical conditions that predispose to bruising or bleeding and should be considered when evaluating for abusive injury.

Ristocetin dependent cofactor activity in von Willebrand disease diagnosis: Limitations of relying on a single measure.

Background: Von Willebrand disease (VWD) is a common inherited bleeding disorder, however the diagnosis can be complicated by a subjective bleeding history and issues with some current von Willebrand factor (VWF) laboratory assays. Objectives: In the Zimmerman Program, we sought to determine how often a type 1 diagnosis was based on a single low VWF ristocetin cofactor (VWF:RCo) level resulting from the common genetic variant p.D1472H or an isolated assay issue, if that low value was corroborated by the VWF glycoprotein-IbM (VWF:GPIbM) assay, and if retesting confirmed original levels. Methods: New patients being evaluated for bleeding were consented. Analysis included VWF sequencing, bleeding scores, and comparisons of local VWF antigen (VWF:Ag) and VWF:RCo to central VWF:Ag and VWF:GPIbM. Results: A total of 18% of VWD subjects had a low local VWF:RCo, but normal VWF:Ag and normal central testing including VWF:GPIbM. Seventy percent of the low VWF:RCo cohort had no pathogenic VWF variants; however, 33% carried p.D1472H. Low VWF:RCo subjects with follow-up local testing within 2 years showed those with p.D1472H continued to have low VWF:RCo and VWF:RCo/VWF:Ag ratio with normal VWF:GPIbM. Subjects without p.D1472H had an increase mean VWF:RCo, resulting in 59% with normal levels on repeat testing. Conclusions: The diagnosis of VWD based on a single low VWF:RCo but normal VWF:Ag, was often attributed to p.D1472H or variability in VWF:RCo that was eliminated with VWF:GPIbM. Our study suggests that using VWF:RCo alone for diagnostic purposes may be insufficient while repeat VWF:RCo or VWF:GPIbM testing can be valuable in establishing a VWD diagnosis.

Evaluation for Bleeding Disorders in Suspected Child Abuse.

Bruising or bleeding in a child can raise the concern for child abuse. Assessing whether the findings are the result of trauma and/or whether the child has a bleeding disorder is critical. Many bleeding disorders are rare, and not every child with bruising/bleeding that may raise a concern for abuse requires an evaluation for bleeding disorders. However, in some instances, bleeding disorders can present in a manner similar to child abuse. Bleeding disorders cannot be ruled out solely on the basis of patient and family history, no matter how extensive. The history and clinical evaluation can be used to determine the necessity of an evaluation for a possible bleeding disorder, and prevalence and known clinical presentations of individual bleeding disorders can be used to guide the extent of laboratory testing. This clinical report provides guidance to pediatricians and other clinicians regarding the evaluation for bleeding disorders when child abuse is suspected.

Laboratory variability in the diagnosis of type 2 VWD variants.

Essentials Patients with von Willebrand disease were enrolled in our study. Type 2 VWD diagnoses were based on original test results. Repeat evaluation resulted in many patients receiving a different type 2 diagnosis. Some genetic variants were particularly likely to move type 2 subcategories. ABSTRACT: Introduction Type 2 von Willebrand disease (VWD) refers to patients with a qualitative defect in von Willebrand factor. Accurate diagnosis of type 2 VWD subtypes can be challenging. Aim of the study To compare the historical diagnosis of type 2 VWD with current laboratory testing. Methods Subjects were enrolled in the Zimmerman Program either because of a preexisting diagnosis of VWD (retrospective cohort) or from evaluation for bleeding symptoms or suspected VWD (prospective cohort). Original diagnosis was assigned by the local center and central diagnosis was based on central laboratory testing. Results Two hundred and seventeen index cases in the retrospective cohort and 35 subjects in the prospective cohort carried a local diagnosis of type 2 VWD (29% and 6% of enrolled index cases, respectively). In the retrospective cohort, the diagnosis was confirmed in 66% of cases with a preexisting diagnosis of 2A, 77% 2B, 54% 2M, and 72% 2N. In the prospective cohort, 31% were confirmed 2A, 60% 2B, 23% 2M, and 100% 2N. Several genetic variants were repeatedly implicated in subjects with changed diagnosis: p.M1304R, p.R1315C, p.R1374C, and p.R1374H. Conclusions Both the prospective and retrospective cohorts demonstrated consistent variation in subjects whose diagnosis changed between 2A, 2B, and 2M. The importance of accurately diagnosing type 2 VWD may be most significant in the 2B subtype given potential concerns with the use of desmopressin in type 2B VWD. Some genetic variants appear in multiple types of VWD, making specific diagnoses challenging.

Prophylaxis versus episodic treatment to prevent joint disease in boys with severe hemophilia.

BACKGROUND: Effective ways to prevent arthropathy in severe hemophilia are unknown. METHODS: We randomly assigned young boys with severe hemophilia A to regular infusions of recombinant factor VIII (prophylaxis) or to an enhanced episodic infusion schedule of at least three doses totaling a minimum of 80 IU of factor VIII per kilogram of body weight at the time of a joint hemorrhage. The primary outcome was the incidence of bone or cartilage damage as detected in index joints (ankles, knees, and elbows) by radiography or magnetic resonance imaging (MRI). RESULTS: Sixty-five boys younger than 30 months of age were randomly assigned to prophylaxis (32 boys) or enhanced episodic therapy (33 boys). When the boys reached 6 years of age, 93% of those in the prophylaxis group and 55% of those in the episodic-therapy group were considered to have normal index-joint structure on MRI (P=0.006). The relative risk of MRI-detected joint damage with episodic therapy as compared with prophylaxis was 6.1 (95% confidence interval, 1.5 to 24.4). The mean annual numbers of joint and total hemorrhages were higher at study exit in the episodic-therapy group than in the prophylaxis group (P<0.001 for both comparisons). High titers of inhibitors of factor VIII developed in two boys who received prophylaxis; three boys in the episodic-therapy group had a life-threatening hemorrhage. Hospitalizations and infections associated with central-catheter placement did not differ significantly between the two groups. CONCLUSIONS: Prophylaxis with recombinant factor VIII can prevent joint damage and decrease the frequency of joint and other hemorrhages in young boys with severe hemophilia A. (ClinicalTrials.gov number, NCT00207597 [ClinicalTrials.gov].).

Low VWF levels in children and lack of association with bleeding in children undergoing tonsillectomy.

von Willebrand disease is a common bleeding disorder, but diagnosis can be difficult in young children who have not had bleeding challenges. We sought to evaluate the correlation between bleeding and von Willebrand factor (VWF) levels in children undergoing surgical challenge with tonsillectomy. Children ages 0 to 18 undergoing tonsillectomy without a personal or family history of bleeding were enrolled prospectively following informed consent and institutional review board approval. VWF levels were obtained at the time of surgery. VWF antigen (VWF:Ag) and VWF activity (VWF:GPIbM) were tested via enzyme-linked immunosorbent assay. Bleeding score was calculated using the International Society of Hematology bleeding assessment tool (BAT). Surgical and postoperative bleeding were determined using questionnaires filled out by the surgeon and patient/family. A total of 1399 subjects were enrolled with evaluable data, with a median age of 5 years. The median VWF:Ag was 85 IU/dL and the median VWF:GPIbM was 100 U/dL. Median BAT for the entire population was 0, including those with postoperative bleeding. There was no difference in VWF level between those who experienced postoperative bleeding and those who did not, with median VWF:Ag 85 vs 85 (P = .89) and mean VWF:GPIbM 98 vs 100 (P = .5). Interestingly, there was a difference in VWF levels with age, with median VWF:Ag 81 for those younger than 3 years, 82 for those 3 to 6 years, 90 for those 7 to 10 years, and 100 for those 11 to 18 years. A similar trend was noted for VWF:GPIbM. Of the 2 to 6 year olds, 5% had VWF:Ag <50, which would meet criteria for low VWF, but only 1.8% had an abnormal BAT at study entry and only 2.5% bled after surgery. Only 1 subject with low VWF had an elevated postoperative BAT >2. These data suggest that low VWF levels do not correlate with bleeding in children undergoing tonsillectomy. In addition, VWF levels outside the adult normal range in young children may be more common than previously thought and do not necessarily predict surgical bleeding.

One year follow-up of children and adolescents with chronic immune thrombocytopenic purpura (ITP) treated with rituximab.

BACKGROUND: We previously showed in a prospective study that rituximab appears to be effective in some children and adolescents with severe chronic immune thrombocytopenia. Eleven of 36 patients achieved and maintained platelet counts over 50,000/mm(3) within the first 12 weeks. These patients were followed for the next year. METHODS: Platelet counts were monitored monthly and all subsequent bleeding manifestations and need for further treatment was noted. RESULTS: Eight of the 11 initial responders maintained a platelet count over 150,000/mm(3) without further treatment intervention. Three patients had a late relapse. One initial non-responder achieved a remission after 16 weeks, and two additional patients maintained platelet counts around 50,000/mm(3) without the need for further intervention. CONCLUSIONS: Rituximab resulted in sustained efficacy with platelet counts of 50,000/mm(3) or higher in 11 of 36 patients (31%).

Recombinant tissue plasminogen activator may reduce frequency of central venous access device infection in hemophilia patients undergoing immune tolerance therapy.

Many patients with hemophilia, particularly those with inhibitory antibodies, utilize central venous access devices (CVADs) to facilitate frequent infusions. Infection of these devices is a common complication of factor replacement therapy. This communication reports our center's experience with CVAD infection in three patients with severe hemophilia A undergoing immune tolerance therapy (ITT) in whom intermittent infusions of recombinant tissue plasminogen activator (rTPA, Cathflo Activase) were utilized. In this small experience, patients experienced a decreased frequency of gram-positive infections when receiving routine rTPA treatments. Larger randomized trial should be performed in this patient population at high risk of CVAD infection.

Von Willebrand disease in the United States: perspective from the Zimmerman program.

This article will discuss the diagnosis and management of von Willebrand disease (VWD) in the United States and results from the Zimmerman Program, a national study of VWD. An algorithm is presented to show how we currently approach diagnostic testing for VWD, including the potential replacement of the ristocetin cofactor assay with a new von Willebrand factor (VWF)-GPIb binding assay. Results from the Zimmerman Program type 1 cohort are presented, including the findings that genetic defects in the VWF gene are most common with VWF levels <30 IU/dL, but bleeding symptoms were present across the entire cohort regardless of VWF level. Typical management of VWD patients is also discussed, including the use of desmopressin and VWF concentrates. Despite these advances, there remain several areas of VWD where more research is required to optimize treatment.

Clinical uses of plasma and plasma fractions: plasma-derived products for hemophilias A and B, and for von Willebrand disease.

The use of plasma-derived factor products to treat hemophilia A, hemophilia B, and von Willebrand disease (vWD) has changed since the start of the human immunodeficiency virus (HIV) epidemic. The use of plasma-derived factor concentrates for hemophilias A and B has decreased in developed countries because of the availability of recombinant products. However, in developing countries, which encompass most of the world's hemophilia community, plasma-product-based therapy remains the backbone of treatment because of economic constraints. Viral attenuation strategies have resulted in a much safer product profile. vWD product selection is less complicated than for hemophilas A and B because plasma-derived products are the only choice for patients who are unresponsive or who cannot receive pharmacologic therapy. As the majority of patients in the world with hemophilias A, B and vWD are treated with plasma-derived clotting factors, the need for these safe and efficacious therapies will continue in the future. This chapter discusses safety strategies for plasma-derived clotting factor, its availability, economics, efficacy, and inhibitor formation.