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Willebrand disease, acquired

Von Willebrand's disease (vWD) is the most common hereditary coagulation abnormality described in humans. It arises from a qualitative or quantitative deficiency of von Willebrand factor (vWF), a multimeric protein that is required for platelet adhesion. It is known to affect humans and, in veterinary medicine, dogs. more...

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Willebrand disease, acquired
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The various types of vWD present with varying degrees of bleeding tendency. Severe internal or joint bleeding is rare (only in type 3 vWD); bruising, nosebleeds, heavy menstrual periods (in women) and blood loss during childbirth (rare) may occur.


When suspected, blood plasma of a patient needs to be investigated for quantitative and qualitative deficiencies of vWF. This is achieved by measuring the amount of vWF in a vWF antigen assay and the functionallity of vWF with a glycoprotein (GP)Ib binding assay, a collagen binding assay or, a ristocetin cofactor (RiCof) activity assay. Factor VIII levels are also performed as factor VIII is bound to vWF which protects the factor VIII from rapid break down within the blood. Deficiency of vWF can therefore lead to a reduction in Factor VIII levels. Normal levels do not exclude all forms of vWD: particularly type 2 which may only be revealed by investigating platelet interaction with subendothelium under flow (PAF), a highly specialistic coagulation study not routinely performed in most medical laboratories. A platelet aggregation assay will show an abnormal response to ristocetin with normal responses to the other agonists used. A platelet function assay (PFA) will give an abnormal collagen/adrenaline closure time but a normal collagen/ADP time. Type 2N can only be diagnosed by performing a "factor VIII binding" assay. Detection of vWD is complicated by vWF being an acute phase reactant with levels rising in infection, pregnancy and stress.

Other tests performed in any patient with bleeding problems are a full blood count (especially platelet counts), APTT (activated partial thromboplastin time), prothrombin time, thrombin time and fibrinogen level. Testing for factor IX may also be performed if hemophilia B is suspected. Other coagulation factor assays may be performed depending on the results of a coagulation screen.

Classification and types


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Platelet function disorders
From Gale Encyclopedia of Medicine, 4/6/01 by Julia Barrett


Platelets are elements within the bloodstream that recognize and cling to damaged areas inside blood vessels. When they do this, the platelets trigger a series of chemical changes that result in the formation of a blood clot. There are certain hereditary disorders that affect platelet function and impair their ability to start the process of blood clot formation. One result is the possibility of excessive bleeding from minor injuries or menstrual flow.


Platelets are formed in the bone marrow--a spongy tissue located inside the long bones of the body--as fragments of a large precursor cell (a megakaryocyte). These fragments circulate in the bloodstream and form the first line of defense against blood escaping from injured blood vessels.

Damaged blood vessels release a chemical signal that increases the stickiness of platelets in the area of the injury. The sticky platelets adhere to the damaged area and gradually form a platelet plug. At the same time, the platelets release a series of chemical signals that prompt other factors in the blood to reinforce the platelet plug. Between the platelet and its reinforcements, a sturdy clot is created that acts as a patch while the damaged area heals.

There are several hereditary disorders characterized by some impairment of the platelet's action. Examples include von Willebrand's disease, Glanzmann's thrombasthenia, and Wiskott-Aldrich syndrome. Vulnerable aspects of platelet function include errors in the production of the platelets themselves or errors in the formation, storage, or release of their chemical signals. These defects can prevent platelets from responding to injuries or from prompting the action of other factors involved in clot formation.

Causes & symptoms

Platelet function disorders can be inherited, but they may also occur as a symptom of acquired diseases or as a side effect of certain drugs, including aspirin. Common symptoms of platelet function disorders include bleeding from the nose, mouth, vagina, or anus; pinpoint bruises and purplish patches on the skin; and abnormally heavy menstrual bleeding.


In diagnosing platelet function disorders, specific tests are needed to determine whether the problem is caused by low numbers of platelets or impaired platelet function. A blood platelet count and bleeding time are common screening tests. If these tests confirm that the symptoms are due to impaired platelet function, further tests are done-- such as platelet aggregation or an analysis of the platelet proteins-- that pinpoint the exact nature of the defect.


Treatment is intended to prevent bleeding and stop it quickly when it occurs. For example, patients are advised to be careful when they brush their teeth to reduce damage to the gums. They are also warned against taking medications that interfere with platelet function. Some patients may require iron and folate supplements to counteract potential anemia. Platelet transfusions may be necessary to prevent life-threatening hemorrhaging in some cases. Bone marrow transplantation can cure certain disorders but also carries some serious risks. Hormone therapy is useful in treating heavy menstrual bleeding. Von Willebrand's disease can be treated with desmopressin (DDAVP, Stimate).


The outcome depends on the specific disorder and the severity of its symptoms. Platelet function disorders range from life-threatening conditions to easily treated or little-noticed problems.


Inherited platelet function disorders cannot be prevented except by genetic counseling; however, some acquired function disorders may be guarded against by avoiding substances that trigger the disorder.

Key Terms

A condition in which inadequate quantities of hemoglobin and red blood cells are produced.
Bone marrow
A spongy tissue located within the body's flat bones-- including the hip and breast bones and the skull. Marrow contains stem cells, the precursors to platelets and red and white blood cells.
The substance inside red blood cells that enables them to carry oxygen.
A large bone marrow cell with a lobed nucleus that is the precursor cell of blood platelets.
Fragments of a large precursor cell (a megakaryocyte) found in the bone marrow. These fragments adhere to areas of blood vessel damage and release chemical signals that direct the formation of a blood clot.

Further Reading

For Your Information


  • Ware, J. Anthony, and Barry S. Coller. "Platelet Morphology, Biochemistry, and Function." In Williams Hematology, edited by Ernest Beutler et al. New York: McGraw-Hill, Inc., 1995.
  • Williams, William J. "Classification and Clinical Manifestations of Disorders of Hemostasis." In Williams Hematology, edited by Ernest Beutler et al. New York: McGraw-Hill, Inc., 1995.


  • Liesner, R. J., and S. J. Machin. "Platelet Disorders." British Medical Journal 314, no. 7083 (1997): 809.

Gale Encyclopedia of Medicine. Gale Research, 1999.

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