Heit, John A.

Abstract Introduction: Assays of plasma von Willebrand factor (VWF) ristocetin cofactor activity (VWF:RCo) are essential for the laboratory diagnosis of von Willebrand disease (VWD). However, the current manual platelet aggregation/aggregometry method has relatively poor operating characteristics. Our goal was to develop a simple, accurate and sensitive platelet based assay. Methods: VWF protein from normal or patient plasma was first captured on the polyclonal anti-VWF antibody coated plastic plate surface. VWF:RCo activity was assayed by the binding of mitotracker (a red fluorochrome)-labeled, formalin-fixed normal platelets in the presence of ristocetin (1mg/ml) and under agitation (200 rpm by vortex). The fluorescence from the bound platelets, measured by a fluorescence microtiter plate reader (Fluor4000, BioRad), was related to the calibrator plasma signal (6∼150% or IU/dL), and reported as % or IU/dL. We tested plasma samples from normal donors (n=16) and known VWD patients (type 1, n=6; type 2, n=9) based on clinical history and levels of plasma VWF antigen (VWF:Ag), VWF:RCo activity (manual platelet aggregation/aggregometry method), factor VIII activity and VWF multimer analysis. Results: For both normal donors and VWD patients, VWF:RCo activities by the plate assay vs. manual platelet aggregation/aggregometry method correlated closely (R2=0.84), and VWF:RCo/VWF:Ag ratios did not differ significantly. Platelet binding to VWF-coated plastic wells is both VWF specific and ristocetin dependent. Conclusions: Although this new platelet based VWF:RCo plate assay is still being optimized and validated, the preliminary data suggest that it is simple, accurate and sensitive.

Abstract Confinement to a nursing home (NH) is an independent risk factor for VTE and accounts for 13% of all VTE occurring in the community, but the question of which NH residents are at risk is largely unanswered. Objective: To determine VTE risk factors among NH residents. Methods: Using the Minnesota State Case Mix Review Program Public Research Files, we performed a case-control study of all Olmsted County, MN NH patients with an ICD-9 code-identified diagnosis of VTE from 1988–1994. From the same source, we identified one age-, sex-matched control and used conditional logistic regression to estimate odds ratios for an association of VTE with 46 characteristics assessed in the Minnesota Case Mix data. Results: Univariate associations between characteristics and odds of VTE are described below. Significantly increased odds were observed for residents assessed following hospitalization (a nearly 4-fold increase, p=0.002, Table) and residents considered incapable of self-preservation (i.e., unable to cope with potentially harmful situations) (> 2.0 fold increase, p=0.03). Non-significant 2–3 fold increased odds were observed for limitations in certain specific Activities of Daily Living (ADL) (including walking and dressing) and for limitations in more than 3 ADLs. Similar increased odds were observed for residents using a wheelchair, taking more than 3 oral medications, enrolled in professional activity programs, and needing behavior management. Conclusions: Need for assistance (especially problems with immobility), lack of self preservation, and recent hospitalization may identify a subset of NH residents that are at especially high VTE risk and who may warrant consideration of prophylaxis. Univariate VTE Risk Factors for Nursing Home Residents Characteristic Odds Ratio 95% CI P-value Oral medications > 3 3.00 0.97-9.30 0.06 Activities of Daily Living High/Medium (4-8) vs. low (0-3) 2.20 0.76-6.33 0.14 Help dressing 2.75 0.88-8.64 0.08 Help walking 3.00 0.61-14.86 0.18 Wheelchair use 2.50 0.97-6.44 0.58 Needs behavior management 3.00 0.62-14.86 0.18 Help toileting 2.00 0.68-5.85 0.20 Lack of self-preservation 2.33 1.07-5.10 0.03 Transfer from hospital 3.86 1.68-8.86 0.0015 Anti-depressant drugs 0.50 0.19-1.33 0.16 Professional activity program 2.25 0.69-7.3 0.18

Abstract Aims/Objective:Congenital antithrombin (AT) deficiency, estrogen-containing oral contraceptive pills (OCPs) and pregnancy are associated with increased risk of venous thromboembolism (VTE). Little is known about reproductive decision-making in women with AT deficiency. We sought to explore the attitudes and choices regarding reproductive health in this population. Study Design/Methods:We conducted a provider-administered survey of women identified from the Mayo Clinic congenital AT deficiency database. Participants were asked to discuss their diagnosis of AT deficiency (age at diagnosis and VTE history including diagnosis and treatment) and questioned about (1) any lifetime methods of contraception, (2) pregnancies and pregnancy outcomes, (3) use of assisted reproductive technology, (4) history of menorrhagia, and (5) how their AT diagnosis had impacted each reproductive health experience and how this impact made them feel (open-ended question). Results:Of 31 women with congenital AT deficiency, 18 (58%) were reached, 8 (26%) were not reachable and 5 (16%) were deceased. Of the 18 women who completed the survey, median age at AT deficiency diagnosis was 40 years (range 7 - 65). Twelve (67%) women had experienced a VTE; 2 and 5 women had VTE in the setting of pregnancy OCP use, respectively. Reported contraceptive methods included OCPs, intrauterine device (IUD), and male condoms. Of the 5 women diagnosed with AT deficiency while taking OCPs, three switched to IUD, one to condoms, and one did not report an alternative method of contraception. Fifteen (83% ) women reported at least one pregnancy (median number of pregnancies = 2; range 1 - 6). Of 42 total pregnancies among the 18 women, 33 (79%) resulted in live term birth, 3 (7%) in live preterm birth, and 6 (14%) in miscarriage/spontaneous abortion at a median of 12 weeks into the pregnancy. Four women (22%) reported the use of anticoagulation during pregnancy (presumed to be low molecular weight heparin, but most women could not specify), and 1 woman reported use of assisted reproductive technology leading to a successful pregnancy. Eleven women (61%) reported menorrhagia, 4 (36%) while on anticoagulation for VTE events. Ten of 18 women (56%) reported that the AT deficiency diagnosis had affected their reproductive health in at least one way. Patient-reported comments are presented in Table 1, and a "word cloud" diagram (an image composed of words from the women's comments regarding contraception), in which the size of each word indicates its frequency) is presented in Figure 1. Conclusion:Women with AT deficiency require careful multidisciplinary management to avoid complications in the settings of hormonal contraception and pregnancy. Many women reported that their reproductive health experiences were impacted by their diagnosis, but also reported successful pregnancy outcomes. Validated questionnaires should be developed to assess women's reproductive health experiences. Strategies for reproductive risk management should be discussed carefully, and patient involvement in reproductive decision-making is key in this population. Word Cloud depicting frequency of women's comments regarding AT deficiency and contraception Word Cloud depicting frequency of women's comments regarding AT deficiency and contraception Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Abstract Introduction: Hospitalization-associated VTE attack (incident plus recurrent VTE) rates over the 6-year period, 2005-2010, did not change significantly despite achieving near-universal in-hospital VTE prophylaxis; 75% of these VTE events occurred after hospital discharge with a median of 19.5 days from hospital discharge to VTE. The median durations of hospitalization and in-hospital prophylaxis were 3 days and 70 hours, respectively, suggesting that VTE prophylaxis was inadequate. However, the hospital population that would benefit most from post-hospitalization VTE prophylaxis is uncertain. Our study aim was to test hospital length of stay (LOS) as a potential predictor of post-hospital-discharge incident or recurrent VTE. Methods: Using the resources of the Rochester Epidemiology Project, we identified all unique Olmsted County, MN residents hospitalized at least once at a Rochester, MN Mayo Clinic hospital and all such residents with objectively-diagnosed occurrence of first or recurrent VTE during hospitalization or within 92 days after hospital discharge, 2005-2010. We tested LOS as a potential predictor of post-hospital-discharge VTE (conditional on surviving to hospital discharge free of VTE) using the Anderson-Gill version of Cox regression modeling and adjusting for age, sex, any surgery performed during that hospitalization, and Charlson Comorbidity Index calculated from conditions recorded from 1/1/2005 until the day of hospital discharge. Results: Over the period, 2005-2010, 31,588 unique Olmsted County residents were hospitalized at least once at a Rochester Mayo Clinic hospital. The distribution of LOS was: 1-2 (3.8%), 3 (24.2%), 4 (23.3%), 5 (16.4%), 6 (8.8%), 7-9 (12.4%), 10-19 (8.4%) and 20+ (2.3%). Of the 253 VTE events identified within 92 days post-hospital discharge, 6, 29, 31, 38, 38, 53, 42 and 16 had been hospitalized for 1-2, 3, 4, 5, 6, 7-9, 10-19 and 20+ days, respectively. The hazard ratios (HR) for post-hospital-discharge VTE were similar for hospital LOS ≤4 days; compared to LOS ≤3 days, the HRs were significantly increased for hospital LOS of 5 (HR=1.78), 6 (HR=2.86), 7-9 (HR=2.71), 10-19 (HR=3.16) and 20+ (HR=4.20) days (Table 1). Conclusions: The adjusted hazards of post-hospital discharge VTE for hospital LOS > 4 days were significantly increased 1.8 to 4.2-fold compared to LOS ≤3 days, suggesting that hospital LOS may be useful for identifying hospitalized patients suitable for longer duration VTE (including post-discharge) prophylaxis. Future studies should be aimed at identifying additional predictors of post-hospital-discharge VTE such that extended prophylaxis can be targeted to those patients who would benefit most. Disclosures No relevant conflicts of interest to declare.

Abstract Abstract 3404 Background: Appropriate periprocedural management of the chronically-anticoagulated patient with an inherited or acquired thrombophilia is uncertain. Objective: To estimate the 3-month cumulative incidence of thromboembolism (TE) and major bleeding and test thrombophilia as a potential predictor of these outcomes among chronically-anticoagulated patients undergoing a procedure. Methods: 2182 consecutive patients referred to the Mayo Thrombophilia Center for standardized peri-procedural anticoagulation management were followed for TE, major bleeding and survival. The three-month cumulative incidence rates for TE, major bleeding and death were estimated by Kaplan-Meier analyses. For each chronic anticoagulation indication, we tested “strong” thrombophilia (antithrombin, protein C or protein S deficiency, homozygous or combined heterozygous Factor V Leiden or prothrombin G20210A), ”weak” thrombophilia (heterozygous Factor V Leiden or prothrombin G20210A), lupus anticoagulant/antiphospholipid antibodies and bridging heparin as potential predictors of TE and major bleeding using Cox proportional hazards modeling. Results: Patients with thrombophilia tended to be younger with a slight female predominance. Compared to no thrombophilia, thrombophilia patients (n=202; 143 bridged with heparin) had similar rates of venous (0% vs. 0.5%; p=0.34) and arterial (0.5% vs. 0.5%; p=0.94) thromboembolism, major bleeding (2.0% vs. 2.0%; p=0.97) and mortality (1.5% vs. 2.2%; p=0.52). Among thrombophilia patients, the TE and major bleeding rates were similar for strong (n=29) or weak thrombophilia (n=99), or lupus anticoagulant/antiphospholipid antibodies (n=74). Similarly, among thrombophilia patients, bridging heparin did not affect the rates of major bleeding (2.1% vs. 1.7%; p=0.85) or TE (0.7% vs. 0%, p=0.52). Conclusions: Inherited or acquired thrombophilia does not appear to impact the rates of TE, major bleeding or mortality after temporary interruption of chronic anticoagulation for an invasive procedure. Disclosures: No relevant conflicts of interest to declare.

Background The incidence of VTE in African-Americans (AAs) is similar to or higher than in Americans of European ancestry. However, the carrier frequencies of inherited thrombophilias common in whites (i.e., Factor V Leiden, Prothrombin G20210A) are very low in AAs, suggesting that other inherited thrombophilias may be associated with VTE in AAs. Objective To identify potentially novel non-hypothesis-driven single nucleotide polymorphisms (SNPs) associated with VTE in AAs. Methods We used the resources of the eMERGE Network to perform a GWAS of VTE in AAs. The eMERGE Network (funded by NHGRI) is comprised of nine sites each with DNA biobanks linked to electronic health records (EHRs). Approximately 39,206 unique DNA samples have been genotyped using either Affymetrix or Illumina genome-wide SNP arrays. Led by the Coordinating Center and eMERGE genomics workgroup, an imputation pipeline was developed for merging genomic data across the different SNP arrays used by the eMERGE sites, to maximize sample size and the power to detect associations. The imputation was performed using the 1000 Genomes Cosmopolitan reference panel which includes 1092 individuals and over 36 million SNPs. From our previously-identified cohort of Olmsted County, MN residents with incident or recurrent VTE, 1996-2005, we derived and validated an EHR-driven phenotype extraction algorithm that leveraged structured data based on ICD-9-CM codes and unstructured data from clinical notes via natural language processing to identify VTE cases and controls with 100% and 94% positive and negative predictive values, respectively. We tested for an association between each SNP and VTE among AAs using unconditional logistic regression, adjusting for age, sex and eMERGE site. Results Among 294 AA VTE cases and 3,661 AA controls (total n=3,955; females, n=2,512), the Factor V Leiden (F5 rs6025) was not analyzed due to a very low minor allele frequency (MAF=0.0036). The prothrombin G20210A (F2 rs1799963) and ABO blood type O (ABO rs8176719) SNPs were not genotyped in any of the arrays and could not be imputed. Among SNPs with an imputation score >0.8, the most significant SNPs associated with VTE were ITPR3 (inositol 1,4,5-triphosphate receptor type 3) rs2229637 (OR=1.65; p=3.61E-07; MAF=0.19) and CLEC7A (C-type lectin domain family 7, member A) rs59819090 (OR=2.16; p=1.06E-06; MAF=0.056). ITPR3 SNPs have been associated with coronary artery aneurysm in Kawasaki disease, type 1 diabetes mellitus and other autoimmune disorders. CLEC7A rs59819090 encodes for a serine82 to leucine nonsynonymous amino acid change in dectin-1. Dectin-1 is a transmembrane innate immune pattern recognition receptor on myeloid cells that upon binding it’s agonist, β-glucans, stimulates cytokine production and the respiratory burst, a prerequisite for formation of neutrophil extracelluar traps (NETs). NETs have been associated with VTE (van Montfoort, et al. Ateriosclero Thromb Vasc Biol 2013;33:147-51). Dectin-1 serine82 is not evolutionarily conserved and the serine82 to leucine amino acid change is predicted to be tolerated, with a moderate effect on protein function. Conclusions ITPR3 rs2229637 and CLAC7A rs59819090 may be associated with VTE in African-Americans. These observations require replication and functional studies toward understanding how they may lie on the causal pathway to VTE. Disclosures: No relevant conflicts of interest to declare.

Abstract Background: Active cancer without or with chemotherapy is associated with a 4- to 6.5-fold increased risk for VTE 1. However, cancer-associated VTE incidence may be under- or overestimated by reports that linked cancer registry data to an anticoagulation clinic database or to hospital discharge diagnosis codes 2–5. Objective: To estimate the incidence of VTE in active cancer in a well-defined geographic population that includes the full spectrum of VTE events (including rapidly fatal events) occurring in the community. Methods: Using the longitudinal resources of the Rochester Epidemiology Project and Mayo Clinic Tumor Registry, we identified all Olmsted County, MN residents with incident VTE by review of their complete medical records in the community 6, and all residents with active cancer (by cancer site), over the 28-year period, 1973–2000. Using residents with active cancer within the three months prior or subsequent to incident VTE as the numerator, and all residents with active cancer as the denominator, we estimated the incidence of VTE in active cancer, both overall and for the subsets of pancreatic cancer, brain cancer and lymphoma. Results: Over 78,236 active-cancer person-years, 595 Olmsted County residents developed incident VTE. The overall active cancer-associated VTE incidence was 760 per 100,000 person-years (95% CI: 701, 824), about 6.5-fold higher than the general population 7. Over 473, 983 and 4,258 pancreatic cancer, brain cancer and lymphoma person-years, respectively, 51, 18 and 46 residents developed incident VTE. The pancreatic cancer-, brain cancer- and lymphoma-associated VTE incidence rates were 10,784 (95% CI: 8029, 14,179), 1,831 (95% CI: 1085, 2,893) and 1,080 (95% CI: 791, 1,441) per 100,000, respectively. Overall, cancer-associated VTE incidence increased with age, and for all ages, men had a higher VTE rate than women. We observed a much higher pancreatic cancer-associated VTE incidence than previously reported. Conclusions: The incidence of VTE in individuals with active cancer (especially pancreatic cancer) is higher than the general population. The incidence of VTE in patients with pancreatic cancer is higher than previously estimated.

Abstract Abstract 709 Background: A recent analysis of merged genome-wide and candidate gene genotypes in VTE cases and controls identified multiple tag SNPs that were strongly associated with VTE. Objective: To identify rare and/or novel functional variants by sequencing the implicated genes. Methods: Cases (n=1488) were Mayo Clinic European-American patients of non-Hispanic ancestry with objectively-diagnosed VTE in the absence of active cancer, venous catheter or antiphospholipid antibodies. Controls (n=1439) were Mayo Clinic outpatients without VTE who were frequency-matched on case age, gender, race, MI/stroke status and state of residence. For this analysis, we selected a subset of these cases and controls for sequencing to take advantage of the joint configuration of two ABO SNPs of primary interest, rs8176719 (ABO exon 6 deletion determining type O blood group) and rs2519093 (ABO intron 1 tag SNP), which were previously shown to be strongly associated with VTE (p=5.7E-12 and p=3.0E-16, respectively). We randomly sampled 82 cases and 14 controls within 3 of the 9 potential allele frequency cells (Figure). The rs8176719 alleles are -−/−- (double deletion is the common allele), –/G, and G/G (the rare allele). The rs2519093 alleles are GG (G is the common allele), AG, and AA (A is the rare allele). For each SNP, the genotypes are represented as 0, 1, or 2 copies of the minor allele. We represented the joint allelic configuration of the two SNPs with the number of copies of the rs8176719 given first as 0/0 (both with 0 copies of the minor allele), 0/1, 0/2 (0 copies of the rs8176719 SNP), 1/0 (1 copy of the rare rs8176719 SNP), 1/1/, and 1/2, and 2/0 (2 copies of the rare allele for the rs8176719 SNP and 0 copies of the rare allele of the rs2519093 SNP), 2/1, and 2/2. From the Figure one observes discrepancies between cases and controls at the 0/0, 1/1 and 2/2 combinations. We randomly sampled from these three combinations, taking one third of the case series. For each SNP, we had 28 cases with 0/0 copies of the rare allele, 27 cases with 1/1 copies of the rare allele; and 27 cases with the combination of 2/2 copies of the rare allele. We compared these 82 cases with 14 controls that do not have any of these combinations. Sixteen genes were selected for deep sequencing, including 5 genes harboring SNPs significantly associated with VTE (F5, SLC19A2, ABO, NME7, ATP1B1), 10 genes with SNPs marginally associated with VTE (C1orf114, KLKB1, SELP, F11, SCUBE1, PRKCB1, CD44, ITPR1, GFRA1, BLZF1), and CYP4V2 which reportedly confounds F11 and KLKB1. Agilent SureSelect probes were designed to capture and enrich the ∼2 Mb genomic regions of these 16 genes. Samples were multiplexed (12-plex) and sequenced using Illumina HiSeq 2000. The sequence reads were aligned to the human genome build 36 using Burrows-Wheeler Aligner, and the single nucleotide variants (SNVs) and small INDELs were called using SNVMix and GATK, respectively. For this analysis, novel ABO SNVs were tested for an association with VTE using age-, sex-adjusted logistic regression and Fisher's Exact Test. Results: 98% of the targeted regions were sequenced with > 20X coverage. On average, ∼2500 SNVs and ∼200 INDELs were detected in each sample. Fifteen novel SNVs in intron 6 and 3' of the ABO gene were associated with VTE (p<E-06) and belonged to 3 distinctive LD blocks; none were in LD with the coding or tag ABO SNPs (rs8176719; rs2519093). SNVs inside the middle LD block at the 3' of ABO are located within an enhancer and promoter histone marked with putative transcription factor binding sites. In addition, strong evidence from both ENCODE and dbEST support the middle LD block as lying within a novel transcript, probably an extension of the 3' of ABO. In addition, we discovered a novel, significant, protective, frame-shifting single base (G) deletion at ABO chr9:135120877. Conclusion: Novel ABO functional variants that are associated with VTE were identified by deep sequencing. Disclosures: Heit: Daiichi Sankyo: Consultancy, Honoraria.

Abstract Background: Compared to Whites, Black-Americans may have a 40% higher incidence of idiopathic VTE. However, whether other VTE characteristics vary by race is uncertain. Objective: To compare demographic and baseline characteristics among White- and Black-Americans with VTE. Methods: Using a standardized data-collection form, demographic and baseline characteristics were prospectively collected from consecutive consenting patients enrolled in seven Thrombosis and Hemostasis Centers from August 2003 to March 2008. For patients with objectively diagnosed VTE, demographic and baseline characteristics were compared among White- and Black-American VTE patients, both overall, and by age and gender. Results: Among 1960 White- and 368 Black-Americans with VTE, compared to Whites, Blacks had significantly less isolated DVT (73.9% vs. 86.5%, p<0.001) and significantly more PE ± DVT (45.1 vs. 39.6%, p=0.05). Blacks and Whites did not differ in mean age (43.4 vs. 44.3 years), but a significantly higher proportion of Black men VTE patients were in age groups 20–39 and 80+ years. Blacks and Whites differed significantly by gender, with a significantly higher proportion of Black women with VTE (69.8% vs. 59.1%, p=0.0001). Blacks had a significantly higher mean BMI (32.3 vs. 29.4 kg/m2, p<0.0001), a significantly lower proportion with recent surgery or trauma, active cancer and infection, and a significantly lower proportion with a family history of VTE or documented thrombophilia (solely due to reduced Factor V Leiden and Prothrombin G20210A prevalence). Conversely, Blacks had a significantly higher proportion with hypertension, hyperlipidemia, diabetes mellitus, chronic renal disease and dialysis, HIV and sickle cell disease. The two races did not differ significantly regarding the proportion with idiopathic VTE, CHF, CAD/MI, peripheral artery disease, stroke or other chronic neurological disease (i.e., cerebral palsy), chronic liver disease or autoimmune disease, including antiphospholipid syndrome. Compared to White women VTE patients, Black women VTE patients had a significantly lower proportion with recent surgery, trauma, infection, oral contraceptive use and possibly hormone therapy; and a significantly higher proportion with idiopathic VTE, hypertension, diabetes mellitus, chronic renal disease, HIV and sickle cell disease. Compared to White men VTE patients, Black men VTE patients did not differ significantly regarding recent surgery, trauma, cancer, infection or autoimmune disease, but Black men had a significantly higher proportion with hypertension, diabetes mellitus, HIV and sickle cell disease. Black and White men with VTE did not differ significantly regarding idiopathic VTE, CHF, CAD/MI, stroke, peripheral arterial disease and chronic renal disease. Conclusion: White- and Black-Americans with VTE differ significantly regarding demographic and baseline characteristics that may be risk factors for VTE.

Abstract Accurate measurement of plasma von Willebrand factor (VWF) activity is essential for the laboratory diagnosis and treatment monitoring of von Willebrand disease (VWD). Currently available VWF activity assays include VWF ristocetin cofactor activity by manual light transmission platelet aggregometry (VWF:RCo–Agg) or flow cytometry (VWF:RCo–FL), collagen I and III binding activity (VWF:Co–I and –III) (Technozym), and platelet activity by latex agglutination (VWF:Lx) (Instrumental Laboratory). In this study we evaluated and compared the accuracy and precision of these 5 assay methods. Plasma samples from 11 normal donors and 41 patients categorized as type 1 (n=20) or type 2 (n=21) VWD based on clinical evaluation, fVIII:C activity, VWF:RCo–Agg, VWF antigen (VWF:Ag) level and plasma VWF multimer analysis by agarose gel electrophoresis were assayed for VWF activity by VWF:RCo–FL, VWF:Co–I, VWF:Co–III and VWF:Lx methods. The VWF:Ag/VWF activity ratio by VWF activity assay method was calculated for each sample. For normal donors and type I VWD patients, VWF:RCo–FL and VWF:Lx correlated well with VWF:RCo–Agg (R2=0.87, and 0.97, respectively), while VWF:Co–I and –III were lower compared to VWF:RCo-Agg. For type 2 VWD patients, different VWF:Ag/VWF activity ratio cutoffs (range 0.3–0.7) were used (Figure). Both VWF:RCo–Agg and –FL were sensitive (95%) and specific (97%) for type 2 VWD while the VWF:Lx was slightly less sensitive (81%) but was very specific (100%). VWF:Co–I and –III were the least sensitive (<90%) and specific (<90%); both methods had high false positive and negative rates for type 2 VWD. In Summary, for normals and type 1 VWD patients, VWF:RCo–FL and VWF:Lx correlate well with VWF:RCo–Agg and have similar sensitivities and specificities for type 2 VWD. VWF:Co–I and –III are unreliable for assessing plasma VWF activity.