von Willebrand Disease

01Pathophysiology

Von Willebrand factor is a large multimeric glycoprotein produced by endothelial cells (stored in Weibel-Palade bodies) and megakaryocytes (stored in platelet alpha granules). It serves two essential hemostatic functions, and understanding both of them is the key to understanding every clinical feature and lab finding in this disease.

Function 1: Platelet adhesion. When a blood vessel is injured, subendothelial collagen is exposed. vWF binds to this collagen and simultaneously binds to the glycoprotein Ib (GP Ib) receptor on platelets, acting as a molecular bridge that tethers platelets to the damaged vessel wall. This is the initial step of primary hemostasis. When vWF is deficient or dysfunctional, platelet adhesion fails, which is why the bleeding pattern in von Willebrand disease mirrors that of platelet disorders: mucocutaneous bleeding such as epistaxis, gingival bleeding, easy bruising, and menorrhagia. The bleeding time is prolonged because platelet plug formation is impaired.

Function 2: Factor VIII carrier and stabilizer. vWF binds to Factor VIII in the circulation and protects it from proteolytic degradation by activated protein C and other proteases. Without vWF, Factor VIII is rapidly cleared from the plasma, leading to a secondary reduction in Factor VIII levels. This is why the PTT is prolonged in von Willebrand disease, even though it is fundamentally a disorder of primary hemostasis. The PT remains normal because the extrinsic pathway is unaffected.

This dual role explains a concept that frequently appears in test questions: von Willebrand disease is a disorder of primary hemostasis (platelet adhesion), yet it also produces a coagulation abnormality (prolonged PTT via Factor VIII reduction). Students who categorize it as purely one or the other will miss questions. The disease sits at the intersection of platelet function and coagulation, and test writers exploit this overlap.

02Classification and Clinical Manifestation

Type 2B is a classic test favorite. It is the only subtype where the platelet count is decreased, creating confusion with thrombocytopenic purpura. The mechanism is a gain-of-function mutation causing vWF to bind platelets spontaneously in circulation, leading to consumption of both large multimers and platelets. Critically, DDAVP is contraindicated in type 2B because releasing more of this abnormal vWF into circulation will worsen platelet consumption and drop the count further.

Type 2N is another high-yield trap. Because vWF antigen and ristocetin cofactor activity are both normal, and the only abnormality is a low Factor VIII, it looks identical to mild hemophilia A on initial testing. The distinguishing feature is the inheritance pattern (autosomal recessive vs. X-linked recessive) and a vWF:Factor VIII binding assay.

03Diagnostic Workup

When a patient presents with mucocutaneous bleeding and a family history of easy bruising, the initial screening panel should include a CBC, PT, PTT, and bleeding time (or PFA-100 closure time). The hallmark screening pattern for von Willebrand disease is a prolonged bleeding time, prolonged PTT, normal PT, and normal platelet count. This combination immediately narrows the differential.

Once this pattern is identified, the confirmatory workup begins with three tests ordered together: vWF antigen level, ristocetin cofactor activity, and Factor VIII activity. The ristocetin cofactor activity is the single most important functional test. Ristocetin is an antibiotic that induces vWF to bind platelet GP Ib in vitro; the degree of platelet agglutination reflects how well vWF functions. A low ristocetin cofactor activity confirms the functional impairment.

For subtyping, ristocetin-induced platelet aggregation (RIPA) is critical. In most types, RIPA is decreased or absent. However, in type 2B, RIPA is enhanced at low concentrations of ristocetin because the mutant vWF has an abnormally high affinity for GP Ib. This is one of the most testable distinctions in the entire workup.

Multimer analysis on gel electrophoresis provides further classification. Loss of high-molecular-weight multimers points to type 2A or 2B. If the multimer pattern is normal but ristocetin cofactor activity is disproportionately low relative to the antigen, type 2M is suspected.

A useful concept for exam preparation: if a vignette shows a patient with a bleeding pattern like hemophilia A (prolonged PTT, low Factor VIII) but the patient is female or has autosomal recessive inheritance, always consider type 2N von Willebrand disease before accepting a hemophilia A diagnosis. The vWF:Factor VIII binding assay will resolve this.

One important caveat: vWF is an acute-phase reactant and can be transiently elevated by stress, exercise, estrogen use, pregnancy, and inflammation. Testing should be repeated on multiple occasions, and samples should be drawn when the patient is at baseline to avoid false negatives.

04Management and Treatment

The cornerstone of type 1 management is desmopressin (DDAVP). DDAVP acts on V2 vasopressin receptors on endothelial cells, triggering exocytosis of Weibel-Palade bodies that release stored vWF and Factor VIII into the circulation. The response is rapid (within 30 to 60 minutes) and typically raises both vWF and Factor VIII levels by 2 to 5-fold. This makes it ideal for minor bleeding episodes and prophylaxis before dental or minor surgical procedures. However, tachyphylaxis occurs with repeated dosing within 24 to 48 hours because endothelial stores become depleted, so its use should be limited to short courses. Patients should also be monitored for hyponatremia due to the antidiuretic effect, particularly children and patients receiving IV fluids.

For patients who do not respond to DDAVP or for whom DDAVP is contraindicated (type 2B, type 3), vWF-containing Factor VIII concentrates are used. Humate-P is the most commonly referenced product. It is a plasma-derived concentrate that contains both vWF and Factor VIII in a ratio that provides physiologic replacement. Dosing is based on ristocetin cofactor units, and the target trough depends on the clinical scenario (minor procedure vs. major surgery vs. life-threatening hemorrhage).

A critical concept: in type 2N, giving recombinant Factor VIII alone (as you would for hemophilia A) is ineffective. The Factor VIII will be rapidly degraded because there is no functional vWF to protect it. You must give vWF-containing concentrates so that exogenous vWF can bind and stabilize the infused Factor VIII. This is a commonly tested distinction.

Antifibrinolytics (aminocaproic acid, tranexamic acid) are important adjuncts for mucosal bleeding. They inhibit plasminogen activation, preventing premature clot dissolution. They are particularly effective for epistaxis, gingival bleeding, and menorrhagia. These agents should not be used simultaneously with prothrombin complex concentrates due to thrombotic risk.

For women with menorrhagia as the predominant symptom, combined oral contraceptives serve a dual purpose: estrogen stimulates hepatic synthesis of vWF (raising baseline levels), and cycle regulation reduces menstrual blood loss. This is frequently tested in a vignette of a young woman with heavy menstrual bleeding and a family history of bleeding.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common way students lose points on von Willebrand disease questions is by confusing it with hemophilia A. Both diseases produce a prolonged PTT and low Factor VIII, so a vignette that provides only these two lab values without mentioning bleeding time or vWF studies is designed to trap you. The critical differentiator is the bleeding pattern: mucocutaneous bleeding (skin, mucous membranes, menorrhagia) points to von Willebrand disease, while deep tissue and joint bleeding (hemarthroses, muscle hematomas) points to hemophilia A. Always check the sex and inheritance pattern in the stem as well. A female patient with a prolonged PTT and bleeding symptoms should raise immediate suspicion for von Willebrand disease, not hemophilia A.

A second common trap involves type 2B and DDAVP. Test writers love to present a patient with von Willebrand disease and mild thrombocytopenia, then offer DDAVP as an answer choice. Students who do not recognize the thrombocytopenia as a signal for type 2B will select DDAVP and get the question wrong. The correct answer is vWF-containing Factor VIII concentrate. Remember: thrombocytopenia in the setting of von Willebrand disease equals type 2B, and DDAVP is contraindicated.

A third area of confusion is the ristocetin cofactor activity. Students frequently mix up ristocetin cofactor activity (which measures vWF function) with ristocetin-induced platelet aggregation (RIPA, which tests platelet responsiveness to ristocetin at varying concentrations). In type 2B, ristocetin cofactor activity is decreased, but RIPA is enhanced at low concentrations of ristocetin. These are different tests, and the distinction is testable.

Finally, remember that vWF levels fluctuate. Blood type O individuals have 25 to 30% lower baseline vWF levels than non-O individuals. Stress, pregnancy, oral contraceptive use, and acute illness can all raise vWF levels and produce false-negative results. A single normal result does not exclude the diagnosis. When a vignette describes a patient with a convincing bleeding history but normal initial labs, the next best step is to repeat testing on a separate occasion.

The core competency being tested across all von Willebrand disease questions is pattern recognition: identifying the overlap between platelet-type and coagulation-type bleeding, correctly interpreting the PTT in context, selecting the right subtype based on subtle lab differences, and knowing when DDAVP is safe versus dangerous.