Pediatric Von Willebrand Disease Workup

Screening tests

Screening tests for von Willebrand disease (VWD) include the following:

• Complete blood count (CBC)
• Template bleeding time
• Prothrombin time (PT)
• Activated partial thromboplastin time (aPTT)

Complete blood count (CBC)

Assess platelet number and morphology, which should be normal in most patients with von Willebrand disease, except those with type 2B von Willebrand disease who may have thrombocytopenia.

Template bleeding time

Because it is reasonably well standardized, the template bleeding time is used as a screening test for primary hemostasis. The reference range for the bleeding time in children is longer than that of adults. Results of the bleeding time are affected by many technical factors, such as the direction of the incision and the skill of the technician. Although a bleeding time outside of the reference range may suggest a defect in hemostasis, it is not diagnostic. Similarly, a bleeding time within the reference range does not exclude the presence of such a defect.

Although neither sensitive nor specific for von Willebrand disease, template bleeding time is outside of the reference range in about 50% of patients with type 1 von Willebrand disease. Patients with von Willebrand disease types 2A, 2B, 2M, and 3 often have prolonged bleeding times.

The template bleeding time has largely been replaced by automatic platelet function analyzers (PFAs), such as the PFA-100, the results from which are frequently normal except in the more severe types of von Willebrand disease.

Prothrombin time (PT)

PT is within the reference range in von Willebrand disease.

Activated partial thromboplastin time (aPTT)

Approximately 25% of patients with type 1 von Willebrand disease have aPTT results outside of the reference range. These results may be caused by concurrent deficiencies of other clotting factors in addition to, or rather than, factor VIII (FVIII). The aPTT should be outside of the reference range in patients with severe von Willebrand disease or type 2N von Willebrand disease in whom circulating FVIII levels are very low. Because aPTT and the template bleeding time are insensitive tests for von Willebrand disease, add von Willebrand factor (VWF) activity to the screening tests performed for patients with suspected bleeding disorders (see below).

Specific assays

Specific assays include the following:

• von Willebrand factor levels
• FVIII activity
• von Willebrand factor activity (ristocetin cofactor)
• von Willebrand factor antigen

von Willebrand factor levels

von Willebrand factor levels vary and can be influenced by numerous factors, including stress, inflammation, and blood type. Individuals with type O blood have lower values of von Willebrand factor levels on average, whereas those with type AB blood have higher values of von Willebrand factor.

Day-to-day variation in von Willebrand factor levels is a normal occurrence in the same individual; therefore, a single level within the reference range does not exclude the diagnosis of von Willebrand disease. Also, estrogen levels increase von Willebrand factor and may affect results in adolescent females and women with menorrhagia. Therefore, in the presence of significant bleeding symptoms, testing to rule out von Willebrand disease may need to be repeated several times.

FVIII activity

FVIII activity is variably decreased.

von Willebrand factor activity (ristocetin cofactor)

Ristocetin is an antibiotic that causes von Willebrand factor to bind to and, subsequently, to activate platelets. In the ristocetin cofactor assay, platelets from individuals who are healthy, standard concentrations of ristocetin, and varying quantities of patient or control plasma are used. In individuals who are healthy, platelets rapidly agglutinate in response to ristocetin; however, the presence of plasma von Willebrand factor is necessary for the reaction to occur. The degree of platelet agglutination is proportional to the concentration of von Willebrand factor in the plasma. Several variations of this assay have been developed. Because the result of this assay reflects the functional activity of von Willebrand factor, it is usually called the von Willebrand factor activity. It is variably decreased in von Willebrand disease.

von Willebrand factor antigen

The total plasma concentration of von Willebrand factor protein is measured by one of several assays. The Laurell rocket immunoelectrophoresis technique measures the amount of von Willebrand factor protein in the plasma, whereas radioimmunoassays and enzyme-linked immunoabsorbent assays reflect the number of von Willebrand factor–binding sites. These tests determine the total amount of von Willebrand factor antigen in the plasma but do not reflect its molecular structure and, hence, may be normal in von Willebrand disease variants with abnormal multimers. Therefore, von Willebrand factor antigen is variably decreased.

Multimer analysis

In multimer analysis to determine the physical structure of von Willebrand factor (ie, whether high–molecular-weight multimers are present), plasma is electrophoresed through agarose gel. The presence or absence of high–molecular-weight von Willebrand factor is used to classify von Willebrand disease. Absence or decreased levels of high–molecular-weight von Willebrand factor multimers is consistent with type 2 von Willebrand disease. Further analysis of von Willebrand factor subunits has been performed with sophisticated electrophoretic techniques, resulting in the description of many type 2 variants.

ACOG statement

The American College of Obstetricians and Gynecologists states that von Willebrand disease “and other inherited and acquired disorders of coagulation and hemostasis should be considered in the differential diagnosis of all patients being evaluated for heavy menstrual bleeding, regardless of age,” with the disease commonly being the source of bleeding problems, including heavy menstrual bleeding, in women and adolescent females. ^[16]

However, a study by Jacobson et al reported that of 23,888 postpubertal girls and adolescents identified, using a national claims database, with heavy menstrual bleeding, only 8% (and only 16% with severe heavy menstrual bleeding) were screened for von Willebrand disease. ^[17] .

As previously stated, testing on multiple occasions may be needed to confirm the diagnosis of von Willebrand disease, given the influence of estrogen, stress, and inflammation on von Willebrand factor levels.

In some laboratories, platelet von Willebrand factor analysis is performed. Gene analysis can also be performed for diagnosis.