Von Willebrand Factor Assay: Nursing Guide
Von Willebrand factor assays measure how much VWF protein is present (VWF antigen) and how well it supports platelet adhesion (VWF activity, often reported as ristocetin cofactor or newer GPIb-binding assays). Nurses protect validity through correct citrate collection, medicine review, and timely communication of low results — and must read antigen, activity, and factor VIII together before clearing mucosal procedures or approving NSAIDs.
Contents
Quick Facts
Key Takeaway
A low VWF antigen with a proportionally low activity usually fits a quantitative deficiency pattern, but an abnormally low activity-to-antigen ratio can suggest qualitative von Willebrand disease — neither pattern alone clears.
Specimen & Collection Details
Nurse quick-reference for collection prep that affects result quality.
Light blue top
3.2% sodium citrate (9:1 blood-to-anticoagulant ratio)
Platelet-poor plasma (citrated)
Tube filled to completion per coagulation protocol; follow laboratory minimum plasma volume for VWF antigen and activity assays
Draw when clinically stable; avoid acute illness, recent surgery, or estrogen surge when repeat confirmation is needed per haematology protocol; not affected by fasting
No fasting is required for von Willebrand factor testing
Process to platelet-poor plasma promptly per coagulation protocol; freeze at −20 °C or colder for send-out when not tested immediately
Often same-day in institutions with on-site coagulation testing; typically one to several days for send-out reference laboratories
Coagulation / specialized haemostasis laboratory
What is Von Willebrand Factor Assay?
Von Willebrand Factor Assay measures von Willebrand factor (VWF) in citrated plasma using specialized coagulation assays. VWF antigen (VWF:Ag) quantifies the amount of VWF protein. VWF activity (commonly reported as ristocetin cofactor [VWF:RCo] or newer GPIb-binding assays such as VWF:GPIbM or VWF:GPIbR) evaluates functional ability to support platelet adhesion. National Heart, Lung, and Blood Institute (NHLBI) and subsequent international guidelines recommend the initial VWD panel include VWF:Ag, VWF activity, and factor VIII coagulant activity (FVIII:C) interpreted together.
Overview
Nurses most often see von Willebrand factor orders when patients report easy bruising, heavy menstrual bleeding, frequent nose or gum bleeding, or prolonged bleeding after dental work. The assay is also ordered when platelet function analysis is prolonged, when aPTT is mildly prolonged with a normal prothrombin time, or before surgery in patients with a personal or family history suggestive of von Willebrand disease (VWD).
Because VWF is an acute-phase reactant and rises with pregnancy, inflammation, and oestrogen exposure, a single borderline result may not exclude mild type 1 VWD — repeat testing is common. VWF also stabilises factor VIII in circulation, so low VWF often lowers FVIII secondarily. Nurses support accurate diagnosis through correct citrate technique, documentation of medicines such as aspirin, and coordination with haematology while a complete blood count (CBC) and mucosal bleeding assessment proceed in parallel.
Before collection, confirm the order includes both VWF antigen and activity (and FVIII:C when ordered as a panel), ensure the citrate tube is filled to the marked line, document pregnancy status and recent desmopressin (DDAVP) use, and hold elective dental or surgical procedures until haematology interprets the full panel. Escalate active mucosal haemorrhage, postpartum bleeding, or head trauma immediately — pending VWF results do not delay haemostasis management.
Mucosal Bleeding and VWF Specimen Validity
Von Willebrand factor assays guide VWD diagnosis and procedure planning — but low activity must be read with bleeding history, factor VIII, and the full panel. Invalid citrate specimens or transient VWF elevation from pregnancy or acute illness can mislead clearance decisions for dental, surgical, or obstetric care.
- Active mucosal or postpartum bleeding while VWF panel is pending
- Low VWF activity with elective dental extraction or surgery still scheduled
- NSAID or antiplatelet use without haematology clearance in suspected VWD
- Underfilled citrate tube or delayed processing driving false low activity
Document: panel components, citrate fill and processing, medicines and hormone status, bleeding assessment, VWF values with reference intervals, procedure hold status, haematology notifications, and patient teaching on report-now symptoms.
What VWF Assays Can and Cannot Tell You
This test can help identify:
- Reduced VWF quantity (antigen) and function (activity) consistent with VWD when appropriately collected
- Discordant antigen and activity patterns suggesting qualitative (type 2) disease when ratio is abnormally low
- Secondary low factor VIII parallel to low VWF on the initial NHLBI-recommended panel
- Need for reflex multimer, collagen-binding, or repeat testing when results are borderline
This test cannot:
- Classify every VWD subtype alone — multimer and specialized assays may be required
- Clear invasive mucosal procedures without haematology interpretation and haemostasis plan
- Replace bleeding history, CBC, and platelet function context
- Exclude mild type 1 VWD when a single test is done during pregnancy, oestrogen therapy, or acute inflammation
Citrate Integrity Checks Before VWF Draw
Verify
VWF:Ag, VWF activity, and FVIII:C when ordered together
Light-blue citrate filled exactly to the marked line
Pregnancy, OCP, or HRT documented on requisition
NSAIDs, antiplatelets, DDAVP, and concentrates reviewed
Elective dental, surgical, or obstetric dates noted for hold planning
Active mucosal bleeding assessed before routine draw if haemorrhage present
Clarify before proceeding when:
- Order lists only VWF antigen without activity when VWD is suspected
- Patient is acutely ill, postpartum, or on oestrogen and repeat baseline is needed
- Prior citrate specimen rejected for underfill, clot, or haemolysis
- Elective mucosal procedure is scheduled before panel returns
- Active bleeding requires haemostasis management before or instead of routine sampling
- Draw is from a heparinized line without institutional discard protocol
Reading VWF Antigen, Activity, and FVIII Together
Pair VWF results with mucosal bleeding history, platelet count, aPTT trend, and laboratory activity-to-antigen ratio comments. Haematology interprets subtype; nurses escalate when patterns plus symptoms do not support procedure clearance.
| Panel pattern | What it may suggest | Nursing focus |
|---|---|---|
| Concordant low VWF:Ag and activity with low FVIII | Quantitative deficiency pattern (often type 1) pending confirmation | Procedure hold; bleeding precautions; repeat testing if borderline per haematology |
| Low activity disproportionate to antigen | Qualitative (type 2) pattern per low activity:antigen ratio | Notify haematology; reflex multimer or collagen-binding assays often follow |
| Normal antigen with low activity only | Type 2 VWD possible — ratio interpretation required | Do not reassure patient or clear procedures from antigen alone |
| Transiently normal panel with strong clinical suspicion | Acute-phase or hormonal elevation masking mild type 1 | Support repeat draw when clinically appropriate; maintain precautions if bleeding continues |
On a small screen, swipe or scroll sideways to see the full table.
Initial VWD Panel Patterns Nurses Should Recognize
NHLBI and ASH/ISTH/NHF/WFH guidance emphasize the three-test initial panel. Nurses do not assign subtype labels — they recognize when patterns require haematology follow-up and procedure holds.
| Pattern label (nursing shorthand) | Typical panel direction | Action cue |
|---|---|---|
| Quantitative deficiency pattern | VWF:Ag and activity both low; FVIII often low in parallel | Hold elective invasive care; bleeding teaching; await haematology plan |
| Qualitative (ratio) pattern | Activity lower than expected for antigen level | Escalate for reflex testing; do not diagnose subtype independently |
| Borderline / repeat pattern | Values near lower reference limit with ongoing symptoms | Support repeat panel; maintain precautions until cleared |
| Acute-phase masking pattern | Normal or high VWF during illness or oestrogen exposure | Document context; repeat when stimulus resolves if suspicion persists |
On a small screen, swipe or scroll sideways to see the full table.
VWF Results at the Bedside
| Bedside point | Nursing note |
|---|---|
| Antigen-only trap | Never clear mucosal procedures from VWF:Ag alone — activity and FVIII must be reviewed |
| NSAID alert | Intercept NSAID orders when VWD is suspected — teach acetaminophen unless haematology clears alternatives |
| Dental timing | Coordinate with dentistry when extraction is scheduled — hold until haematology documents haemostasis plan |
| Hormone context | Document pregnancy and OCP status — may require repeat baseline testing |
| Tube fill | Underfilled citrate is a frequent reject — fill to the marked line and mix gently ×6 |
| Assay method | Ask laboratory whether ristocetin cofactor or GPIb-binding activity was used — methods are not interchangeable across sites |
On a small screen, swipe or scroll sideways to see the full table.
Why Von Willebrand Factor Assay is Ordered
Von Willebrand factor assays are ordered when mucosal or cutaneous bleeding suggests a primary haemostasis defect, when family history supports VWD, or when preprocedure screening requires VWF quantitation before invasive care.
| Clinical Indication | What the Test Answers | Nursing Rationale |
|---|---|---|
| Suspected von Willebrand disease with mucocutaneous bleeding | Is VWF quantity or function reduced? | NHLBI and ASH/ISTH/NHF/WFH guidelines describe VWF:Ag plus VWF activity as core initial tests when VWD is clinically suspected. |
| Heavy menstrual bleeding, epistaxis, or gum bleeding with normal platelet count | Does a VWF defect explain mucosal bleeding better than thrombocytopenia? | Mucosal bleeding patterns are classic for VWD; VWF testing follows CBC and often platelet function screening per institutional algorithms. |
| Prolonged or abnormal platelet function analysis (PFA-100 closure time) | Does closure-time prolongation reflect VWF deficiency or dysfunction? | Prolonged CEPI on platelet function analysis frequently triggers VWF antigen and activity confirmation — PFA alone does not diagnose VWD. |
| Preoperative or pre-delivery assessment with bleeding history | Is VWF activity adequate for planned invasive or obstetric care? | Haematology uses VWF activity targets (often toward 50–100% for major surgery per institutional protocol) to plan DDAVP, tranexamic acid, or VWF concentrate. |
Contraindications and Precautions
There is no absolute contraindication to venous blood collection, but invalid specimens or misleading clinical timing require clarification before results drive procedure clearance.
- Underfilled citrate tube — alters blood-to-anticoagulant ratio and can falsely prolong functional VWF assays.
- Sample drawn during acute illness, postpartum period, or active inflammation — VWF may be transiently elevated and mask mild type 1 VWD.
- Heparin-contaminated line draw without appropriate discard — interferes with paired clotting assays and may delay valid VWF interpretation.
- Using VWF antigen alone to clear dental extraction — activity and FVIII must be reviewed with haematology.
- Assuming a normal VWF antigen excludes type 2 VWD — activity-to-antigen ratio and possible multimer analysis are required when activity is disproportionately low.
- Continuing NSAIDs or scheduling mucosal procedures while VWF panel is pending without bleeding precautions.
- Active mucosal haemorrhage, postpartum haemorrhage, or haemodynamic change with known or suspected VWD — escalate per haematology and facility protocol immediately.
- Confirmed low VWF activity before scheduled dental extraction, endoscopy, or surgery without documented haematology clearance and haemostasis plan.
- Head injury or neurological change in a patient with low VWF and bleeding history — urgent assessment pathway regardless of pending send-out results.
Patient Preparation
No fasting is required. Preparation focuses on valid citrate collection, medicine review, pregnancy and oestrogen status documentation, and procedure-hold coordination while the panel is pending.
Pre-test checksReview aspirin, P2Y12 inhibitors, NSAIDs, anticoagulants, oral contraceptives and hormone therapy, desmopressin, tranexamic acid, and VWF-containing factor concentrates. Do not stop prescribed haemostasis therapy without haematology authorization — document last dose and time on the requisition.
Performance — nursing procedure guide
This page is a Tests & Diagnostics guide for Von Willebrand Factor Assay. It emphasizes why the test is ordered, how to interpret results, when to escalate, and preparation factors that affect validity — not step-by-step performance technique (those live under Nursing Procedures when available).
Step-by-step technique, supplies, infection prevention, and immediate post-procedure monitoring for this test are covered in:
Use the Patient preparation, Results and interpretation, and Nursing responsibilities sections on this page for order verification, pre-analytic checks, result follow-up, critical-value escalation, and documentation.
Result follow-up at a glance
Nursing workflow on this page — from order to safe action on results:
Results and Interpretation
VWF antigen and activity are reported as a percentage of normal or as international units per deciliter (IU/dL) when international health authorities-linked calibrators are used. Interpretation requires all three initial tests when ordered together — VWF:Ag, VWF activity, and FVIII:C — plus the activity-to-antigen ratio. NHLBI guidance assay coefficients of variation can reach 10–30%, especially for ristocetin cofactor methods; always use the reporting laboratory reference interval.
Reference ranges, critical values, and protocols may vary by laboratory, institution, patient population, and testing method. Always follow local policy and the reporting laboratory’s reference range.
| Result | Range / Finding | Clinical Meaning | Nursing Action |
|---|---|---|---|
| Within expected range or therapeutic target | Within institutional reference interval for VWF:Ag and VWF activity | VWF quantity and function adequate at time of sample for that laboratory’s reference population (ABO-stratified ranges may apply locally) | Interpret with bleeding history — a normal panel does not override significant mucosal bleeding; repeat or expanded testing may still be ordered per haematology |
| Near therapeutic target / borderline | Low-normal or borderline VWF (near lower reference limit) | May reflect mild type 1 VWD, ABO-related variation, or transient elevation masking deficiency — repeat testing is often required per NHLBI algorithms | Do not clear invasive procedures independently; notify prescriber; arrange repeat VWF panel per haematology when clinical suspicion remains |
| Prolonged / above target | Elevated VWF antigen and/or activity above reference | Often acute-phase response, pregnancy, oestrogen use, or recent stress — may temporarily mask mild type 1 VWD rather than indicating a bleeding disorder | Interpret with clinical context; note timing of illness or hormones; repeat when acute stimulus resolves if mild VWD is still suspected |
| Shortened / below target | Below reference interval (decreased VWF:Ag and/or activity) | Consistent with VWD or acquired von Willebrand syndrome when confirmed; disproportionately low activity relative to antigen suggests type 2 pattern per NHLBI ratio thresholds (commonly below 0.5–0.7, laboratory-specific) | Notify haematology; apply mucosal bleeding precautions; hold NSAIDs and elective invasive procedures until clearance; arrange reflex multimer or confirmatory testing per laboratory comment |
Low VWF Results, Procedure Holds, and Escalation
Universal numeric critical values for VWF assays are not specified as a single standard threshold in the published references. Escalation is driven by active bleeding, obstetric haemorrhage, preprocedure low activity, and haematology protocol — not by one number alone. Reference intervals and critical call thresholds vary by laboratory, ABO type, and assay method.
| Critical Finding | Threshold / Value | Immediate Action |
|---|---|---|
| Active mucosal or postpartum bleeding with low VWF activity | Haemorrhage with confirmed or suspected low VWF panel | Escalate according to facility policy; activate haemostasis pathway with haematology — do not defer treatment for pending send-out results |
| Low VWF activity before imminent invasive procedure | Dental, surgical, or obstetric procedure scheduled without haemostasis plan | Notify prescriber and haematology immediately; hold procedure until documented clearance and treatment plan (DDAVP trial, antifibrinolytic, or concentrate per orders) |
| Head trauma with known VWD or low FVIII/VWF | Mechanism or symptoms concerning intracranial bleeding | Urgent haematology and emergency pathway per institutional protocol — treat as high-risk bleeding regardless of last VWF percentage |
Stop routine workflow and escalate according to facility policy when the patient has uncontrolled mucosal bleeding, postpartum haemorrhage, head injury with bleeding diathesis, or a scheduled invasive procedure without haematology clearance after a low VWF activity result.
Factors Affecting Results
VWF assays are sensitive to pre-analytic quality, ABO blood type, hormonal status, and acute illness. Nurses prevent misinterpretation through correct citrate technique, medicine documentation, and timely communication of discordant patterns.
- Transiently normal or elevated VWF during pregnancy, oestrogen therapy, or acute-phase illness — may falsely reassure when type 1 VWD is present
- Normal VWF antigen with missed disproportionately low activity — type 2 VWD requires ratio interpretation, not antigen alone
- Assuming low FVIII confirms haemophilia A without VWF testing — VWD types 2N and 3 can lower FVIII secondarily
- Borderline low VWF dismissed because bleeding is attributed only to thrombocytopenia or anaemia without full panel review
- Single normal VWF activity after DDAVP trial interpreted as lifelong normal without repeat baseline testing
- Prolonged PFA closure time attributed solely to aspirin without VWF confirmation when both may contribute
- ABO blood group (type O often has lower baseline VWF)
- Pregnancy, oral contraceptives, and acute inflammatory states
- Recent DDAVP, VWF concentrate, or cryoprecipitate — document timing relative to draw
Von Willebrand factor assays do not classify every VWD subtype alone — type 2 often requires activity-to-antigen ratio interpretation and reflex multimer or collagen-binding assays per laboratory algorithms. Assay variability between ristocetin cofactor and newer GPIb-binding methods is substantial; results must be interpreted with the reporting method and reference interval. The panel cannot replace bleeding history, platelet disorders, or factor deficiencies that may coexist. Always follow local escalation policy and haematology interpretation.
Nursing Responsibilities
Nursing responsibilities emphasise valid citrated specimens, medicine and procedure-hold coordination, mucosal bleeding surveillance, and clear communication of low or discordant VWF patterns to haematology.
Before the TestDocumentation
Documentation should link specimen quality, medicine history, bleeding assessment, VWF panel values with reference intervals, and prescriber or haematology communication.
“VWF panel specimen collected 09:40 — light-blue citrate filled to line, inverted ×6, frozen aliquot per coagulation protocol. 28-year-old with heavy menses and bruising; dental extraction on hold pending results. Not pregnant; ibuprofen PRN last dose yesterday — nurse held repeat NSAID dose and taught acetaminophen alternative per protocol. Results 16:20: VWF:Ag 32%, VWF:RCo 28%, FVIII 38% (all below laboratory reference). Haematology notified; read-back documented; mucosal bleeding precautions reinforced; multimer analysis pending.”
- Indication, panel components ordered, and specimen processing compliance
- VWF:Ag, VWF activity, FVIII:C values with laboratory reference intervals
- Activity-to-antigen ratio comment when provided by laboratory
- Medicines (NSAIDs, antiplatelets, DDAVP) and pregnancy or hormone status
- Procedure hold status and haematology or prescriber notifications
- Bleeding assessment, patient teaching, and pending reflex assays
Patient and Family Education
Patients with suspected VWD need practical explanation of what the blood tests measure and what bleeding symptoms require urgent review.
Von Willebrand Factor Assay NCLEX practice questions
Practice NCLEX-style clinical judgment focused on Von Willebrand Factor Assay safety and nursing judgment. Use the case tabs (orders, results, assessment, nursing notes), then answer eight Next Gen–style items (including an ordered workflow step) and evaluate outcomes with the answer key.
Select a tab to view orders, results, assessment, and nursing note details for this case.
- Order: Von Willebrand panel — VWF:Ag, VWF:RCo, FVIII:C (citrated plasma)
- Indication: 28-year-old with heavy menstrual bleeding, easy bruising, and prolonged CEPI on platelet function analysis; elective dental extraction in 4 days
- Timing: Morning draw; not pregnant; no acute illness today
- Related orders: CBC with platelet count; repeat VWF panel if borderline per haematology; VWF multimer analysis if reflex ordered; type and screen if transfusion pathway needed
- Result: VWF:Ag 32%, VWF:RCo 28%, FVIII:C 38% (all below laboratory reference); activity-to-antigen ratio concordantly low; platelets 210 × 10⁹/L
- Trend / prior value: Hgb 10.8 g/dL with microcytic pattern; aPTT 38 s (slightly prolonged); prior CEPI prolonged — VWF panel confirms quantitative deficiency pattern pending subtype workup
- Pending tests: VWF multimer analysis; haematology consult before dental extraction; DDAVP trial decision pending specialist review
- Vital signs: HR 88/min, BP 118/70, RR 16/min, SpO₂ 99% on room air, Temp 36.8 °C
- Symptoms: Heavy menses requiring pad changes hourly on peak days; scattered forearm bruises; intermittent gum bleeding with brushing; denies headache or abdominal pain
- Focused assessment: Pale conjunctivae; no active epistaxis; oral mucosa without petechiae; joints without swelling; cooperative and anxious about pending dental procedure
- Preparation notes: Citrated tube filled to line; ibuprofen PRN for cramps last taken yesterday — nurse counselled on NSAID avoidance; acetaminophen supplied per protocol
- Collection events: Peripheral draw successful; specimen accepted by coagulation laboratory; dentist office called to confirm extraction on hold until haematology plan documented
- Teaching gaps / safety concerns: Low concordant VWF panel with scheduled dental extraction; anaemia; recent NSAID use; patient asking whether extraction can proceed because platelet count is normal
Answer key & rationale
Frequently Asked Questions
FAQ
What is the difference between VWF antigen and VWF activity?
VWF antigen measures the amount of von Willebrand factor protein in plasma. VWF activity (often reported as ristocetin cofactor or a GPIb-binding assay) measures how well that protein supports platelet adhesion. NHLBI and international guidelines recommend both together with factor VIII activity for initial VWD evaluation.
Does a patient need to fast before von Willebrand factor testing?
No special fasting is usually required for the citrated VWF panel unless other tests on the same draw require fasting. Follow the ordering clinician’s instructions and local laboratory policy.
Can one normal VWF result rule out von Willebrand disease?
Not always. VWF rises with pregnancy, oestrogen, inflammation, and acute stress, which can temporarily normalize mild type 1 VWD. Haematology may order repeat testing when clinical suspicion remains. Type 2 patterns also require activity-to-antigen ratio interpretation, not antigen alone.
Why is factor VIII measured with the VWF panel?
VWF stabilises factor VIII in circulation. Low VWF often lowers FVIII secondarily, and comparing all three results helps distinguish VWD patterns from isolated factor deficiencies per NHLBI initial testing recommendations.
Should nurses clear dental or surgical procedures when VWF is low?
No. Nurses communicate low or discordant results to the prescriber and haematology, maintain bleeding precautions, and follow documented hold plans. Haemostasis targets and treatment (desmopressin, tranexamic acid, or VWF concentrate) are specialist decisions.
What medicines should be reviewed before VWF testing?
Review aspirin, other antiplatelet agents, NSAIDs, anticoagulants, hormonal therapy, and recent desmopressin or VWF-containing products. Document medicines on the requisition; do not stop prescribed therapy without prescriber or haematology authorization.
When should nurses escalate before VWF results return?
Escalate according to facility policy for active mucosal bleeding, postpartum haemorrhage, head injury, haemodynamic change, or scheduled invasive procedures without a haemostasis plan when VWD is suspected — pending laboratory results do not delay treatment of significant bleeding.
References
References
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National Heart, Lung, and Blood Institute. The Diagnosis, Evaluation and Management of von Willebrand Disease. Bethesda (MD): NHLBI, NIH.https://www.nhlbi.nih.gov/health-topics/diagnosis-evaluation-and-management-of-von-willebrand-disease
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James PD; et al. Clinical and laboratory diagnosis of von Willebrand disease: A synopsis of the 2008 NHLBI/NIH guidelines. Haemophilia. 2016.https://pmc.ncbi.nlm.nih.gov/articles/PMC5592788/
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Leebeek FWG; Eikenboom JCJ. Von Willebrand disease: update on laboratory diagnosis and management. Hematology Am Soc Hematol Educ Program. 2021.https://pmc.ncbi.nlm.nih.gov/articles/PMC10439443/
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Centers for Disease Control and Prevention. Bleeding Disorders in Women — Von Willebrand Disease. Atlanta (GA): CDC.https://www.cdc.gov/bleedingdisorders/women/vwd.html
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Konkle BA; et al. Von Willebrand Disease. GeneReviews® [Internet]. Seattle (WA): University of Washington; 1993 (updated 2023).https://www.ncbi.nlm.nih.gov/books/NBK7014/
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Lassila R; et al. How I treat von Willebrand disease. Blood. 2021; American Society of Hematology education series.https://doi.org/10.1182/blood.2020007890
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National Hemophilia Foundation. Von Willebrand Disease — Diagnosis. New York (NY): NHF.https://www.hemophilia.org/bleeding-disorders-a-z/types/von-willebrand-disease/diagnosis
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World Federation of Hemophilia. Von Willebrand disease. Montreal (QC): WFH.https://wfh.org/en/what-is-hemophilia/all-about-hemophilia/von-willebrand-disease
Editorial Standards & Medical Review
About the author: Sid A. Abdala Balal, RN, writes evidence-based nursing education focused on diagnostic safety, clinical interpretation, and bedside nursing judgment.
Medical review: This guide is reviewed by Dr. Adam Sayedi, MD, for clinical accuracy, diagnostic safety, and alignment with current standards for Von Willebrand Factor Assay.
Policies: Medical Review Process · Editorial Policy · Correction Policy