Von Willebrand disease is caused by a deficiency in von Willebrand factor, which helps platelets stick together to form clots. It is usually inherited through mutations in the VWF gene. The disease impairs the initial formation of platelet plugs and stabilization of clots. Treatment focuses on replacing or increasing von Willebrand factor through drugs or transfusions to control bleeding issues. Research is ongoing to determine the best management of surgical cases in patients with the disease.

1. Von Willebrand Disease: Overview, Prevalence, Treatment, and Current Research
Dylan Djani
BIOSC 467 Principles of Hematology
April 26, 2013

2. Abstract
Von Willebrand disease involves a decrease in the blood levels of von Willebrand factor,
which represents a clotting disorder due to the lack of platelet aggregation and corresponding
diminished blood levels of Factor VIII. Von Willebrand disease is more often caused by
inherited mutations than issues secondary to other disease processes, and specific details of the
inherited mutations and subsequent phenotypic effects characterize types and subtypes of the
disease. Types of hereditary von Willebrand disease and treatment options are relatively
consistent between humans and dogs. Treatments include drug and transfusion therapy aimed at
increasing circulating levels of von Willebrand factor and Factor VIII, but other options are
available in order to control bleeding issues. Current clinical research is being conducted to
determine the best ways to manage surgical cases in patients with von Willebrand disease,
although each individual has a unique disease presentation in that different drugs and transfusion
products may show more efficacy than others.

3. Introduction
Blood is a type of connective tissue in the animal body in that blood consists of cells
suspended in a matrix of plasma and includes erythrocytes, leukocytes, and thrombocytes or
platelets (1). The importance of blood is inherently illustrated in its function in transportation:
blood is responsible for transporting nutrients, wastes, gases, hormones, heat, cells, and proteins
throughout the entire animal body (2). Every single cell of the animal body requires nutrients
and generates metabolic waste products and thus must be accessible by blood in order to
continue living. Blood gains access to tissues of the body by existing and circulating through
specific vessels in the body that, along with the heart, make up the vascular system (3). Starting
at the heart blood flows into arteries, which branch into smaller arterioles and eventually the
characteristically thin capillaries. Blood flows out of the capillaries into larger venules and
eventually veins, which feed the blood back into the heart. Transport and exchange between
cells of the body and the blood occur at the level of the capillary. The structure of the capillary
reflects its function in that the vessel wall is the thinnest of all vessels, consisting of a single
layer of cells. The walls of all vessels in the vascular system facing the lumen are generally
referred to as the vascular endothelium and also have multiple critical functions. Maintaining
blood circulation in the closed system of the vasculature at an adequate rate and volume is
quintessential for the survival of the cells that make up the body’s tissues, organs, and organ
systems. The animal body has homeostatic mechanisms in place to prevent blood from escaping
the vasculature when damaged, as well as ways to shut down such mechanisms so as not to
overcompensate (4). Damage to the vascular system results in hemorrhage and, in severe cases
such as trauma or disease, compromises the accessibility of blood to body tissues due to
decreased intravascular blood volume, termed hypovolemic shock. Hemostasis is the

4. homeostatic mechanism involved in preventing blood loss from the vasculature. This
mechanism involves positive feedback and must be strictly regulated in order to prevent
excessive hemostasis or thrombosis, which can also compromise blood’s accessibility to body
tissues by directly blocking circulation.
The overall goal of hemostasis is to regulate blood flow in order to prevent its escape
from the vasculature so that proper physiology can be conserved for survival (5). Hemostasis is
divided into two systems: primary hemostasis and secondary hemostasis (3). Primary hemostasis
involves local vasoconstriction to limit blood flow to the site of damaged vasculature and the
action of platelets to help initially stop blood from flowing out of the vasculature. Secondary
hemostasis results in the formation of a clot at the injured site via a cascade of plasma proteins
called clotting factors that results in blood coagulation. Blood coagulation inherently
incorporates proteins involved in degrading the blood clot after repair of the vascular tissue in
order to resume normal blood flow. The balance of pro-coagulation and anti-coagulation
mechanisms in the body contributes to overall homeostasis.
Von Willebrand Disease is defined as a bleeding disorder associated with the von
Willebrand factor plasma protein, either due to insufficient levels in circulation or a dysfunction
or defect in the factor (6). The negative impacts on hemostasis seen in von Willebrand disease
reflect a lack of the main functions of the von Willebrand factor and are due to inadequate
platelet adhesion or due to a corresponding reduction in the levels of circulating Factor VIII.
Von Willebrand disease is the most commonly inherited bleeding disorder in both humans and
dogs and is caused by an inherited mutation in the VWF gene (7, 8). On the other hand, acquired
von Willebrand disease is rarer than the inherited disease and results in a qualitative deficiency
of circulating levels of von Willebrand factor (9). Potential mechanisms for triggering acquired

5. von Willebrand disease are not fully understood and may involve autoimmune antibodies
targeting von Willebrand factor or tumor cells adsorbing the factor, which diminishes its levels
in circulation and interferes with its roles in hemostasis (10). Subtypes of inherited von
Willebrand disease are used to classify the degree of severity of the disease in both humans and
dogs (6, 8). Considerations in affected patients depend on severity of the disease and are
important in determining how to best manage the disease. Treatments usually vary based on
disease subtype and include drug or transfusion therapy (3).
Primary Hemostasis
Primary hemostasis is a result of the exposure of extravascular collagen as a result of
endothelial damage (11). Initial vasoconstriction occurs due to the removal of normal products
synthesized by healthy endothelium during times of damage, including nitric oxide. Platelets in
circulation undergo platelet adhesion and bind to the exposed collagen through specific platelet
surface receptors and ligands based on the shear force of circulation at the damaged site. If the
damaged site is located at a point in circulation with high shear force, platelet adhesion primarily
occurs via interactions between the collagen, a protein called von Willebrand factor (vWF), and
platelet receptors specific for vWF; however, if the damaged site is at a location with lower shear
force, platelet adhesion occurs mainly through interactions of the proteins fibronectin and
laminin with the exposed collagen. The von Willebrand factor is synthesized and stored by
endothelial cells and platelets, in Weibel-Palade bodies and alpha granules respectively, and
exposure of underlying collagen is one factor that stimulates vWF release. After being released
vWF either stays in circulation or binds to the exposed collagen, the latter of which results in the
release of blood protein Factor VIII and platelet adhesion by virtue of binding vWF-specific
receptors on the platelets. Platelets express a glycoprotein complex called GP Ib-IX-V complex,

6. which adheres platelets to collagen-bound vWF. Adhered platelets, whether via vWF or
fibronectin/laminin, then undergo the process of platelet activation, resulting in a shape change
such that the platelets acquire pseudopodia, releasing of granule contents, and modification of
cell surface expression of molecules (2). However, platelet activation can actually be triggered
in vivo prior to any adhesion in cases of inflammation via the blood protein thrombin, which is
also involved in the coagulation cascade in secondary hemostasis.
Platelets activated by adhering to collagen induce activation and aggregation in more
platelets by releasing stores of ADP and by synthesizing thromboxane A2 and platelet-activating
factor, all of which induce activation by increasing intracellular calcium in the target platelet;
although, the most effective platelet activating has been demonstrated to be thrombin, indicating
the overlap of primary and secondary hemostasis (5). Thromboxane A2 and platelet-activating
factor also further contribute to local vasoconstriction. Activated platelets have an altered GP Ib-
IX-V complex such that an active binding site for the protein fibrinogen is revealed, which is
accompanied by the expression of the GP IIb-IIIa complex due to the shape changes from
activation. These shape changes also result in the exposure of negatively charged phospholipids
on the surface of platelets – mainly phosphatidylinositol and phosphatidylserine. The negative
surfaces of the exposed phospholipids on the surface of platelets as well as damaged endothelial
cells provide a stabilizing microenvironment on which the coagulation cascade of secondary
hemostasis begins (12). After activation, platelets express both GP Ib-IX-V and GP IIb-IIIa
complexes that have the ability to bind vWF and fibrinogen, resulting in the aggregation of
platelets at the damaged site via the formation of vWF and fibrinogen bridges between platelets,
regardless of whether vWF was initially involved in platelet adhesion.

7. The aggregation of platelets results in the formation of a platelet plug that contributes to
hemostasis, albeit being unstable. Once the platelet plug has completely sealed the damaged site,
healthy endothelial cells surrounding the platelet plug are induced to produce prostacyclin, which
has vasodilation effects and inhibitory effects on platelet aggregation. Adhered and activated
platelets can also bind leukocytes passing by in circulation via cross binding of many receptor
complexes, including vWF and the corresponding platelet receptors (13).
Secondary Hemostasis
The ultimate goal of secondary hemostasis is to stabilize the platelet plug via formation
and cross-linking of a fibrin clot at the site of the plug (3). The overlapping extrinsic and
intrinsic pathways of blood coagulation involve protease cascades culminating in the conversion
of prothrombin to thrombin via activation of Factor X and the subsequent cleavage of fibrinogen
into fibrin, resulting in the formation of a fibrin clot (4). The extrinsic pathway of coagulation
involves the release of tissue factor from damaged endothelium, which cleaves and activates
Factor VII to VIIa while also forming complexes with VIIa. The tissue factor-VIIa complex
amplifies the activation of Factor IX to IXa in the intrinsic pathway of coagulation and
contributes the extrinsic tenase complex along with the calcium ion and Factor X on an exposed
phosphatidylserine on the surface of an activated platelet in the platelet plug. The tenase
complex cleaves and activates Factor X to Xa, an activation step common to both the extrinsic
and intrinsic pathways.
The intrinsic pathway involves components of the kallikrein-kinin system and begins
when a spontaneous cleavage event of prekallikrein to kallikrein occurs and is stabilized by the
negative charges of the exposed phospholipids on platelets in the platelet plug, along with
Factors XII, XI, and high molecular weight kininogen (12). The stabilization of these factors is

8. termed contact activation and is referred to as the contact system (5). Kallikrein cleaves and
activates Factor XII to XIIa, which amplifies the conversion of prekallikrein to kallikrein and
thus the entire intrinsic pathway. Factor XIIa also cleaves and activates Factor XI to XIa and
cleaves the molecule bradykinin off of the compound high molecular weight kininogen.
Bradykinin acts as a local vasodilator in order to bring more plasma clotting factors to the site of
coagulation. Factor XIa in conjunction with the calcium ion cleaves and activates Factor IX to
IXa, which is further carried out by the tissue factor-VIIa complex from the extrinsic pathway.
Along with the extrinsic pathway’s tenase complex, the intrinsic pathway forms a version of the
tenase complex as well via Factor IXa, the calcium ion, Factor X, and the activated Factor VIIIa.
Factor VIIIa is a product of the activation of Factor VIII by minute amounts of thrombin and
contributes to the intrinsic tenase complex; increasing amounts of thrombin inactivates VIIIa and
illustrates the self-limiting capacity of thrombin to help regulate the entire coagulation cascade.
The von Willebrand factor also contributes to the stabilization of Factor VIII and serves as a
plasma carrier for this clotting factor (6). The intrinsic tenase complex also results in the
activation of Factor X to Xa, although the intrinsic pathway as a whole in healthy individuals
seems to mainly function in amplifying Factor X activation and having implications in
fibrinolysis.
Both the extrinsic and intrinsic pathways of blood coagulation overlap at the formation of
the tenase comlex and the subsequent activation of Factor X to Xa and contribute to the
conversion of prothrombin to thrombin via the formation of the prothrombinase complex (5).
Similar to the tenase complex, the prothrombinase complex also forms on the negative
phospholipid exposed on the surface of activated platelets; however, the prothrombinase
complex consists of the calcium ion, Factor Xa, Factor Va, and prothrombin. Factor V, like

9. Factor VIII, is activated by minute amounts of thrombin, but is inactivated through the activation
of Protein C to limit thrombin formation (4). The binding of prothrombin is the last event that
occurs in the formation of the prothrombinase complex and results in its cleavage via Factor Xa
into thrombin. Thrombin cleaves soluble plasma fibrinogen into fibrin monomers that
spontaneously arrange to form the initial fibrin clot at the location of the platelet plug. Thrombin
also cleaves and activates Factor XIII to XIIIa, which is a transglutaminase enzyme that
covalently cross-links fibrin monomers to form a stabilized fibrin clot, or thrombus. Thrombin
also has other regulatory functions, such as those described in platelet activation and activation
of other clotting factors. Levels of circulating active thrombin are specifically controlled via
feedback inhibition and the action of thrombin inhibitors, including antithrombin, α2-
macroglobulin, heparin cofactor II, and α1-antitrypsin. Furthermore, thrombin regulation is
achieved via the complexing of thrombin with thrombomodulin, which activates protein C and
serves to inhibit various clotting factors along with protein S. The importance of protein C and
protein S is evident in corresponding genetic deficiencies, which can lead to venous thrombosis.
The formation of fibrin clots in secondary hemostasis is homeostatically balanced
through the process of fibrinolysis (4). Fibrinolysis is mediated through the activity of plasmin,
which is a serine protease responsible for the degradation of fibrin. The inactive form of
plasmin, plasminogen, circulates and binds to fibrin as clots are laid down, such that the
plasminogen must only be activated in order for clot dissolution to occur. Plasminogen
activators include Factor XIIa, tissue plasminogen activator, urokinase, and kallikrein, which are
all kept in check through various activating and inhibiting proteins in order to maintain
coagulation and clot dissolution homeostasis. The intrinsic pathway of coagulation inherently
contains more plasminogen activators than the extrinsic pathway, thus the intrinsic pathway is

10. responsible for proportionately more fibrin degradation (12). Upon degradation, fibrin is cleaved
to form various fibrin degradation products, some of which are of clinical significance.
Etiology and Epidemiology of von Willebrand Disease
Etiologies of von Willebrand disease can be categorized as either hereditary or acquired
based on whether the underlying cause is genetic. The prevalence rate of hereditary von
Willebrand disease is about 1% of the general population in humans, whereas acquired von
Willebrand disease is thought to be very rare due to the low number of documented cases (10).
The VWF gene encodes for the von Willebrand factor and is located towards the distal end of the
short arm of the autosomal chromosome number 12 (6). The large size and boundaries of introns
and exons reflect the nature of the von Willebrand factor, namely it’s large size with multiple
domains that grant the protein its multiple functions. Illustrations of the von Willebrand factor’s
domains emphasize the location of binding sites for Factor VIII, GPIb, heparin, collagen, and GP
IIb-IIIa. Synthesis of the von Willebrand factor involves the initial translation of pre-pro-VWF,
which is cleaved into pro-VWF and eventually VWF before its release from endothelial cells or
platelets (7). Hereditary von Willebrand disease can result from differing mutations along the
entire span of the VWF gene, resulting in a phenotypic spread of severity of the presenting
disease and subsequent difficulty in assigning a single pattern of inheritance. The multiple
possibilities for VWF gene mutations and their inheritance patterns results in various
homozygous and heterozygous genotypes, which means that in some cases people or animals can
be carriers of the disease.
Human hereditary von Willebrand disease is classified into three types based on
phenotypic disease presentation, with type 2 having four subtypes (6). Type I is characterized by
a partial deficiency in the circulating amounts of von Willebrand factor and the highest

11. prevalence rate compared to other types. Type I is associated with an autosomal dominant
inheritance pattern of a mutation that affects intracellular transport of von Willebrand factor or
promotes its rapid clearance from the blood; autosomal dominant meaning that affected
individuals are either homozygous dominant or heterozygous. The lowered levels of plasma von
Willebrand factor may be clinically noted; however, the amount of von Willebrand factor present
is generally enough to maintain platelet adhesion and stabilization of Factor VIII properly, thus
patients with Type I von Willebrand disease are at a low risk for bleeding issues. Type II von
Willebrand disease is characterized by a structural defect in the von Willebrand factor due to a
mutation at a specific location on the VWF gene. The phenotypic results based on the location of
the mutation allow for subtyping of Type II based on the affected domain: IIA results in
decreased platelet adhesion and deficiency of specific multimers, IIB results in increased binding
affinity for GP Ib, IIM results in decreased platelet adhesion without any multimer deficiencies,
and IIN results in a substantial decrease in binding affinity for Factor VIII. In general type II
shows an autosomal dominant pattern of inheritance, but in some cases an autosomal recessive
pattern is seen. The severity of type II is higher than type I in that the propensity to bleed
excessively is increased, which indicates the need for additional medical care by a hematologist.
Type III von Willebrand disease is characterized by virtually undetectable circulating levels of
von Willebrand factor, accompanied by extremely low levels of circulating Factor VIII. Type III
is the rarest of all types and shows an autosomal recessive mode of inheritance. The extreme
disease presentation of type III can often result in severe bleeding episodes and are usually
caused by mutations throughout the VWF gene, commonly sourcing from nonsense or frameshift
mutations.

12. Canine hereditary von Willebrand disease is classified into three subtypes that correspond
with the types of human hereditary von Willebrand disease, but may be interpreted slightly
differently (8). Type I describes low concentrations of von Willebrand factor in the blood with
the presence of all forms of the multimer. Breeds in which type I have been reported include
Dobermans, dachshunds, German shepherds, golden retrievers, and greyhounds. Type II
describes a lowered plasma concentration of von Willebrand factor with a disproportionate
amount of von Willebrand multimers in the blood. Reported breeds for type II include German
shorthaired pointers and wirehaired pointers. Type III describes undetectable amounts of von
Willebrand factor in circulation and has been reported in Scottish terriers and Shetland
sheepdogs. As with human hereditary von Willebrand disease, the severity of the canine
hereditary von Willebrand disease generally increases from type I to type III. Inheritance is
autosomal recessive for types II and III; however, evidence for incomplete dominant and
recessive patterns exists for type I. In most cases type I shows an incomplete dominant
inheritance pattern, with homozygous dominant phenotypes only rarely seen due to periparturient
deaths of the fetus (14).
Acquired von Willebrand disease is often referred to as a syndrome due to its general
associations with underlying diseases such as lymphoproliferative and myeloproliferative
disorders, immunological disorders, and cancers (9). Patients with acquired von Willebrand
disease have the wild-type VWF gene with no mutations with laboratory findings similar to
patients with the hereditary form of the disease, namely a decreased circulating amount of von
Willebrand factor with a lesser degree of decreased circulating Factor VIII levels. The main
pathophysiological mechanisms associated with the acquired von Willebrand disease are an
increased intravascular proteolysis of von Willebrand factor, the formation of autoantibodies

13. against von Willebrand factor, immunoadsorption of von Willebrand factor – Factor VIII
complexes to cancer cells, or a decreased synthesis of von Willebrand factor somehow linked to
hypothyroidism. In humans, acquired von Willebrand disease normally presents more often in
elderly patients, which differs from hereditary forms of the disease (10). In dogs, acquired von
Willebrand disease is also linked to hypothyroidism due to the influence of thyroid hormone
regulation on the synthesis of von Willebrand factor (14). Furthermore, dogs that are carriers of
the von Willebrand disease gene show exacerbated disease signs after the onset of hypothyroid
events, which may also be caused in part by thrombocytopenia secondary to hypothyroidism.
Current Clinical Treatments and Therapies
Patients presenting with bleeding episodes, regardless of whether von Willebrand disease
is the cause, should be initially stabilized and treated for any issues associated with blood loss,
such as anemia or hypovolemic shock (8). Considerations in treating von Willebrand disease
patients include avoiding invasive surgery and the use of drugs with anti-platelet activity due to
the compromised hemostasis in diseased patients. Initial treatment of von Willebrand disease
includes drug therapy and transfusion therapy in both humans and dogs, with the main goal of
increasing circulating levels of von Willebrand factor; however, treatments involved in
stimulating hemostasis without manipulating blood von Willebrand factor levels may also be
used (6).
The drug desmopressin acetate is used in treating mild to moderate von Willebrand
disease due to its stimulatory effects on endogenous von Willebrand factor release from
endothelial cells (6). The drug’s complete name is deamino 8 D-arginine vasopressin (DDAVP)
and functions as a vasopressin analog by agonizing V2 receptors expressed on endothelial cells,
which increases intracellular cAMP levels and triggers the release of Weibel-Palade bodies. The

14. release of endothelial Weibel-Palade bodies results in the release of von Willebrand factor,
Factor VIII, and tissue plasminogen activator, but circulating levels of plasminogen inhibitors
prevent the release of the latter from inhibiting hemostasis. However, the use of DDAVP should
be avoided in patients at risk of cardiovascular disease due to complications involving
thrombosis.
The administration of interleukin-11 (IL-11) has been shown to increase plasma von
Willebrand factor and Factor VIII levels in mouse models with and without von Willebrand
disease, as well as in dogs (15, 16). The studies performed on dogs illustrated that IL-11 and
DDAVP increase circulating levels of von Willebrand factor through different mechanisms in
vivo, which suggest future potential use of IL-11 as supplemental therapy for von Willebrand
disease patients.
Transfusion therapies involve replacing blood lost from bleeding events and introducing
exogenous von Willebrand factor and Factor VIII into the patients (8). Exogenous
administration of von Willebrand factor and Factor VIII concentrates has shown to improve
signs associated with disease and are also used in diseased patients who require invasive surgery
to promote hemostasis (6). Manufactured products of specific ratios of von Willebrand
factor/Factor VIII concentrates include Humate-P and Alphanate SD/HT. Humate-P also
contains fibrinogen and albumin and is indicated for treating spontaneous bleeding or bleeding
from traumatic injuries when the use of DDAVP is contraindicated or not completely effective.
Alphanate SD/HT also contains other plasma proteins and is indicated, along with Humate-P, in
invasive surgeries on diseased patients as prophylaxis. Alphanate SD/HT, however, is not
indicated in patients with type III von Willebrand disease who require major surgery.

15. Other treatments and therapies for von Willebrand disease patients involve the
administration of anti-fibrinolytic drugs and the application of topical agents to promote
hemostasis (6). Anti-fibrinolytic drugs include aminocaproic and tranexamic acids, which
inhibit the activation of plasmin. Such drugs are contraindicated in patients with disseminated
intravascular coagulation or bleeding of the genitourinary tract due to downstream complications
of the drugs. Topical agents include bovine thrombin, fibrin sealants, collagen sponges, and a
zeolite mineral product called QuickClotTM. Fibrin sealants are especially helpful in minor
surgical situations, such as dental surgery.
Current Researchinto Treatments and Therapies: Clinical Trials
Current clinical trials seem to be aimed at testing the effectiveness of various ratios of
von Willebrand factor and Factor VIII concentrates in diseased patients undergoing surgery,
which is pragmatic and geared towards improving survival rates of these patients in surgery.
One study is analyzing the effectiveness of Alphanate concentrates in patients with type III von
Willebrand disease undergoing major surgery (17). The use of Alphanate is currently
contraindicated on patients with type III von Willebrand disease, possibly because studies on the
safety and efficacy of its use have not yet been completed. Another study is analyzing the
efficacy and safety of the product Wilate on patients with hereditary von Willebrand disease who
also require invasive surgeries (18). The product Wilate represents another combination of von
Willebrand factor and Factor VIII to help promote hemostasis during surgery.
Other clinical trials involved with von Willebrand disease include attempting to better
understand how our laboratory methods of measuring hemostasis function in patients with von
Willebrand disease. One such study involves measuring changes in thromboelastography
throughout the menstrual cycle in women (19). Thromboelastography is a newer method of

16. measuring blood coagulation and has shown better results than the traditional PT and aPTT
clotting assays because the latter tests are based on older models of hemostasis.
The last group of current clinical trials involving von Willebrand disease involves the
effectiveness and safety of IL-11 in von Willebrand disease patients. An example of such studies
includes the phase II study of the use of IL-11 in treating type I von Willebrand disease (24).
Another study is analyzing the use of IL-11 in cases of von Willebrand disease that are
unresponsive to DDAVP (20).
Conclusion
Von Willebrand disease involves a decrease in the blood levels of von Willebrand factor
and Factor VIII. The von Willebrand factor is involved in primary and secondary hemostasis by
acting as a ligand for platelet aggregation and by serving as an intravascular carrier protein for
Factor VIII. Diminished levels of von Willebrand factor thus decreases platelet aggregation and
blood levels of Factor VIII, which negatively impacts both primary and secondary hemostasis
and has the potential to cause severe bleeding issues in diseased individuals. Hereditary and
acquired forms of von Willebrand disease have been clinically documented in humans and dogs,
with 1% of the human population having a hereditary form of the disease. However, acquired
forms are thought to be considerably rarer than hereditary forms. Types and subtypes of
hereditary von Willebrand disease are classified based on the specific mutation involved in
decreasing plasma von Willebrand factor levels and the corresponding phenotypic effects of the
mutation. Treatments involve increasing the levels of von Willebrand factor in the blood in
order to promote both primary and secondary hemostasis, which is accomplished through drugs
or through transfusion therapy of fresh plasma or concentrated products. Other treatments
involved in von Willebrand disease are involved in controlling episodes of bleeding, which is of

17. a more immediate concern in order to stabilize patients presenting with bleeding. The use of
transfusion therapy is largely used in promoting hemostasis in von Willebrand disease patients
who require major surgery, and the focus of many current clinical trials is to determine the
effectiveness of various combinations of von Willebrand factor, Factor VIII, and other plasma
protein products to improve survival rates of diseased patients undergoing invasive procedures.

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