Download Administrative Office St. Joseph`s Hospital Site, L301

Administrative Office
St. Joseph's Hospital Site, L301-10
50 Charlton Avenue East
HAMILTON, Ontario, CANADA L8N 4A6
PHONE: (905) 521-6141
FAX: (905) 521-6142
http://www.fhs.mcmaster.ca/hrlmp/
Issue No. 64
QUARTERLY NEWSLETTER
August 2002
Laboratory Diagnosis of
von Willebrand Disease
von Willebrand disease (vWD) is one of the most common inherited bleeding disorders. In recent years, there have been major
advances in our understanding of vWD, which is caused by quantitative and/or qualitative problems with von Willebrand factor
(vWF). Normally, vWF has two important roles in controlling bleeding: it promotes platelet adhesion in the initial steps of
hemostasis, and it functions as the carrier protein for factor VIII (the protein needed for fibrin clot formation that is missing in
patients with severe hemophilia A). Patients who completely lack vWF have combined problems with platelet adhesion and
fibrin clot formation.
vWF is one of the largest known proteins in the body, and is made in both endothelial cells and in megakaryocytes. vWF
circulates in plasma and is also retained within platelets and endothelial cells for release at sites of blood vessel injury. During
hemostasis, vWF supports platelet adhesion by interacting with two platelet receptors, glycoprotein (GP) IbIX and the integrin
aIIbb3. Conformational changes in vWF (induced by shear forces or binding to blood vessels) are thought to initiate the binding
of vWF to platelet GP IbIX. This event triggers further activation of platelets, which allows plasma vWF, and other adhesive
ligands, to bridge platelet aIIbb3 receptors to create a stable platelet plug.
The levels of vWF vary considerably in healthy individuals and are often increased with strenuous exercise, stress, pregnancy,
hemorrhage, and surgery. Low levels are seen in inherited or acquired vWD and in hypothyroidism. vWF levels are influenced
by ABO blood groups. Levels are lowest in blood group O and are highest in blood group AB. Therefore, ABO blood groups
must be considered before making the diagnosis of mild vWD. Because vWF levels can fluctuate, abnormalities should be
confirmed, and several determinations are often needed for suspected mild vWF deficiencies.
The common types of bleeding problems experienced by individuals with vWD are mucocutaneous bleeding symptoms (nose
bleeds, bruising, heavy menstrual periods, postpartum bleeding, bleeding gums, GI bleeding) and immediate excessive
bleeding with trauma, surgery and dental extractions. Severe vWD is associated with platelet-like and hemophilia-like bleeding
symptoms, because of low factor VIII levels. The rare type 2N form of vWD mimics mild-moderate hemophilia because of an
impaired factor VIII binding function of vWF.
The new revised classification scheme divides vWD into three major categories (see chart, Page 2). Types 1 and 3 vWD are
associated with quantitative vWF deficiencies, whereas type 2 vWD is associated with qualitative vWF abnormalities,
subdivided according to the type of changes found. Genetic abnormalities in the vWF gene have been demonstrated in many
forms of type 2 vWD, but are largely unknown in type 1 vWD.
Laboratory Tests Available for the Diagnosis of vWD
The special coagulation laboratory of the HRLMP offers the following tests for the diagnosis of vWD:

vWD screen: Includes tests for factor VIII:C, vWF antigen and vWF ristocetin cofactor activity. If these tests show an
abnormality, multimer testing is performed. ABO blood group should be determined, if unknown, to facilitate
interpretation of the test results. (see Gill et al).

Factor VIII:C level: quantitative assay of the function of coagulation factor VIII in plasma

vWF-antigen assay (vWF:ag): quantitation of the vWF-antigen in the plasma by an enzyme linked immunoassay.

Ristocetin Cofactor Activity assay (RCoF): measures the ability of the patient’s plasma vWF to support aggregation
of standardized test platelets with ristocetin. Normally, the ratio of vWF RCoF to vWF:ag are close to 1 whereas low
ratios (<0.7) are typical of type 2A, 2B and 2M vWD.

vWF multimer analysis: Western blot assay that evaluates the sizes of vWF multimers in the patient’s plasma. Should
be done when vWD screens indicate abnormalities and/or the ratio of vWF RCoF:vWF:ag is <0.7. Multimer patterns are
helpful in distinguishing quantitative and qualitative forms of vWD. Patients with abnormal multimers should have RIPA
testing done.

Ristocetin Induced Platelet Aggregation (RIPA) studies: The RIPA assay evaluates the ability of the patient’s
plasma and platelets to aggregate in response to low and high concentrations of ristocetin. RIPA tests are
recommended when vWD screening tests show an abnormality and/or type 2B vWD is suspected based on initial
investigations and/or family history. Reduced RIPA with high dose ristocetin can be seen in types 1, 2, and 3 vWD, and
in patients with platelet disorders. Abnormally increased RIPA with low dose ristocetin is seen in type 2B vWD, and
much less commonly, in "platelet type vWD" where the platelet GPIbIX has increased vWF binding.

Bleeding time: a standardized cut is made on the forearm and the time to stop bleeding is determined. Test is not
sufficiently sensitive to screen patients for vWD, and is of limited value in investigating vWD.
Classifications of vWD
Classification
Inheritance
Type 1 vWD
autosomal
dominant
Description / variants
quantitative deficiency, below the level
expected for the individual’s ABO blood group
accounts for approximately 70% of vWD
Type 2 vWD
Typ
e 2A
most forms
autosomal
dominant
qualitative abnormalities in vWF
platelet-dependent adhesive function and an
absence of the most potent, high and
intermediate molecular weight vWF multimers
autosomal
dominant
the most common type 2 variant
Typ
e 2B
abnormally affinity of vWF for the platelet
receptor GP IbIX. Unlike type 2A, there is
abnormally platelet aggregation with low dose
(0.5 mg/ml) ristocetin. Often associated with a
lack of the largest vWF multimers.
autosomal
dominant
second most common type 2 variant
Typ
e 2M
autosomal
dominant
platelet-dependent adhesive function with
normal vWF multimers
Typ
e 2N
typically
autosomal
recessive
markedly  affinity of vWF for factor VIII,
resulting in low factor VIII levels
Type 3 vWD
autosomal
recessive
rare
virtually complete deficiency of vWF
Summary table of typical laboratory findings in the different forms of vWD
vWD
Factor VIII
vWF:ag
RCoF
Type 1


 proportionally with
vWF:ag
RIPA
can be  at high conc.,
normal
normal at low dose
 at high conc. relative to
Type 2A
 or normal
 or normal
 relative to vWF:ag
VWF Multimers
vWF:ag,
large and
intermediate
multimers absent
normal at low dose
 or normal;
Type 2B
 or normal
 or normal
Type 2M
 or normal
 or normal
Type 2N
moderately 
normal
typically  relative to
the level of vWF:ag
 relative to the level of
vWF:ag
normal
with low dose; mixing studies
indicate the defect is in the
patient’s plasma
large multimers
usually absent
usually 
normal
normal
normal
Type 3
 ( 5% of normal)
absent or
trace
absent
absent
none or only traces
detected
For further information please contact the Special Coagulation laboratory at 905-521-2100 ext. 76277.
REFERENCES
1.
2.
Colman RW, Hirsh J et al. "Hemostasis and Thrombosis, Basic Principles and Clinical Practice, 4th edition"; Lippincott Williams
and Wilkins; pp 825-837: 2001.
Gill JC, Endres-Brooks J, Bauer PJ, Marks WJ, Montgomery RR. The effect of ABO blood groups on the diagnosis of von
Willebranddisease. Blood 69: 1691-1695, 1987.
Karen A. Moffat, ART, Technical Specialist, Specialized Regional Coagulation Laboratory
Catherine P.M. Hayward, MD, PhD, FRCP(C), Head, Specialized Regional Coagulation Laboratory
HRLMP, Hamilton Health Sciences, McMaster University Medical Centre Site