A von Willebrand’s Disease screen comprises:
- Factor VIII
- von Willebrand’s Antigen (vWAg)
- Ristocetin Cofactor (RICOF)
- Full Blood Count
- Group and Save
Von Willebrand disease (vWD) is the most common hereditary coagulation disorders, although it may also be acquired. The disorder results from a qualitative or quantitative deficiency of von Willebrand factor (vWF), which is a carrier protein for Factor VIII (preventing its proteolytic degradation in plasma) and is also an adhesive protein involved in the interaction between platelets and the endothelial cells lining the blood vessel wall.
There are four hereditary types of vWD which are classified as Type 1, Type 2, Type 3 and Pseudo or platelet-type. Acquired types of vWD have also been described and usually have autoimmune involvement.
Type 1 vWD –Accounts for 60-80% of all vWD cases and is a quantitative heterozygous defect of the vWD gene resulting in decreased production of vWF. Many patients are asymptomatic or have mild bleeding symptoms and the diagnosis of vWD is often incidental and as a result of medical procedures requiring blood work-up.
Type 2 vWD – Accounts for 20-30% of all vWD cases and is a qualitative defect of vWF resulting in structural abnormalities of vW multimers or an absence of subgroups of large or small multimers.
Type 3 vWD – Is the most severe form of vWD and is characterised by a complete absence of vWF. vWF antigen levels are undetectable and factor VIII activity is also very low resulting in potential life threatening haemorrhage.
Platelet-type (pseudo vWD) – vWF is qualitatively normal and genetic analysis of the vWF gene and protein reveal no mutational alteration. The defect is with the GP1 receptor on the platelet membrane which increases its affinity to bind vWF.
Acquired vWD – Is usually the result of an autoimmune disease where antibodies bind to vWF resulting in removal of the vWF-antibody complex from the circulation. Also, some patients with aortic valve stenosis are susceptible to acquired vWD, which may lead to gastrointestinal bleeding (Heyde’s syndrome) and some patients with a left ventricular assist device (LVAD) may have a bleeding tendency due to acquired vWD due to mechanical destruction of large vWF multimers.
Current laboratory (adult, M/F) normal ranges are as follows:
- Factor VIII: 56-174%
- vWAg: 40-150%
- RICOF: 40-150%
The volume of blood in coagulation samples must lie within the volume range as indicated by the size of the black fill arrow present on tubes. Volumes above or below the arrow will result in sample rejection to ensure validity of results.
- Urgent: 4 hours
- Routine: 1 week
Age of sample
Samples will be rejected if received more than 1 hour after venepuncture.
- 4 blue top (sodium citrate) sample.
- All coagulation tubes must be adequately filled (see above).
- All coagulation tubes must be mixed several times by gentle inversion immediately after venepuncture. Mixing the sample with the anticoagulant stops the sample clotting within the tube.
- It is not possible to provide results on clotted, insufficient, haemolysed, or lipaemic samples. These will be rejected with the appropriate comment.
- Sample tubes that have expired cannot be accepted.
Coagulation Lab, James Cook University Hospital, Marton Road, TS4 3BW