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What Do Blood Tests For Von Willebrand Disease Measure?
To help diagnose von Willebrand disease or other bleeding disorders, a doctor will request various blood tests. These tests will measure the presence and activity of certain substances in the blood.
Von Willebrand disease (VWD) is a blood-clotting disorder. It occurs when a person has insufficient or ineffective supplies of a substance in the blood known as von Willebrand factor (VWF). This is a protein that plays an important role in the process of forming a blood clot.
Typically, after an injury where bleeding occurs, VWF in the blood attaches to small blood cells known as platelets. This helps the platelets stick together and form a clot at the site of injury to stop bleeding. However, with ineffective or low levels of VWF, the clot may take longer to form or form incorrectly. This may result in a person experiencing excessive bleeding.
To help diagnose VWD, a healthcare professional will order blood tests. These tests will evaluate the blood for substances in the blood that promote blood clotting. For example, this includes measuring the amount, activity, and structure of VWF.
To help diagnose VWD and other bleeding disorders, a doctor will request a number of blood tests. Typically, a person may need to repeat these tests several times to receive an accurate diagnosis. This is because multiple factors, such as stress, infections, and pregnancy, can affect the levels of clotting factors in the blood.
Read on to learn more about coagulation disorders.
The results of these tests can also help a doctor identify which type of VWD a person has. One test to help diagnose VWD is known as the VWF antigen test.
VWF is a protein in the blood that aids coagulation by acting as a glue that sticks platelets together at the site of injury. Additionally, VWF further affects clotting by influencing the availability of clotting factor VIII, which is another important protein in the formation of blood clotting.
If VWF does not function correctly, or there is too little available, a person is unable to form a platelet plug, or it takes too long to form one. As such, this test measures the amount of VWF and determines how well it functions.
Ristocetin is an antimicrobial substance that binds to VWF and increases its ability to bind to platelets. Therefore, higher levels of ristocetin cofactor results in higher levels of agglutination, or clumping together, of platelets and VWF.
A doctor can use a ristocetin cofactor test to measure the activity of VWF. As such, low levels of ristocetin cofactor have links to lower VWF activity and VWD.
VWF is a multimeric protein, which consists of multiple polypeptide chains, which themselves are chains of amino acids, also known as the building blocks of proteins. These chains help VWF perform its functions of interacting with platelets and factor VIII.
In particular, the activity of VWF depends on the presence of high-molecular weight (HMW) multimers, which have hemostatic ability. The term hemostasis refers to the ability to stop bleeding.
As such, the multimer test measures HMW multimers, as low levels can suggest VWD.
Platelets play an important role in the formation of a blood clot. Specifically, platelets bind to VWF to help form the clot at the site of injury.
As such, platelet function tests can measure the ability to form blood clots and help diagnose blood clotting disorders, such as VWD. In particular, platelet aggregation studies can aid a VWD diagnosis. This test measures how well platelets aggregate, or clump together.
To form a blood blot, VWF must also bind to blood clotting factor VIII to help stimulate the coagulation cascade, which activates proteins that enable clotting. Factor VIII is one of many coagulation factors that also play an important role in hemostasis.
VWF plays a protective role and prevents the breakdown of factor VIII. As such, low levels of VWF have links to a decrease in factor VIII levels. Therefore, it is helpful to measure the amount of factor VIII in the blood when diagnosing VWD.
A deficiency in factor VIII may also relate to hemophilia A, which is another type of bleeding disorder.
Von Willebrand disease is a condition that affects the blood's ability to clot. It occurs due to a deficiency or problem with von Willebrand factor. This is a protein that plays an important role in the initial formation of a blood clot.
To help diagnose the condition, a doctor will order a number of blood tests. These tests will measure the amount, activity, and structure of certain substances, such as von Willebrand factor, in the blood. Low levels or activities of these substances may suggest a person has von Willebrand disease.
Factor VIII Activity Assay
Primary Name Factor VIII Assay Synonym Factor VIII functional assay Synonym Factor VIII activity assay Contraction FVIII Contraction FVIII:C UAB Procedure Number 2500480 CPT Code 85240 Specimen Collect one (1) blue-stopper tube (3.2% sodium citrate), filled to specified volume. Do not underfill or overfill. Specimen Management Note time of collection and time of last treatment if applicable. Centrifuge blue-stopper tube within one (1) hour of collection, separate plasma and test or quick-freeze at -70°C. Specimen Accepted Daily including weekends Test Performed Monday-Friday. Available Stat? Pathologist approval required. Description Congenital factor VIII deficiency, termed hemophilia A, is inherited as a sex-linked recessive and is seen in 1 in 5000 males. Factor VIII deficiency is also seen in some cases of von Willebrand disease.Rare inhibitors (autoantibodies) cause acquired factor VIII deficiency, usually in adults. Factor VIII deficiency is associated with mild to severe bleeding.
Chronic elevated factor VIII confers a 2- to 3-fold risk of venous thrombosis. Because factor VIII is an acute phase reactant, a single elevated result may not alone indicate a risk of thrombosis.
Reference Interval 50-186% Critical Value None Follow-up Test *If von Willebrand disease is suspected, the ristocetin cofactor (vWF activity) and von Willebrand factor antigen assays are recommended. *If an anti-VIII inhibitor is suspected, an inhibitor titer (Bethesda titer) is recommended Associated With Bleeding disorders Associated With Venous thrombosis Associated With Von Willebrand disease © Copyright by the University of Alabama at BirminghamTop of Page
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