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Zorluk: OrtaOrdering Laboratory Tests

A 19-year-old woman is referred to the hematology clinic due to a lifelong history of easy bruising, frequent epistaxis, and heavy menstrual bleeding. She recently underwent a dental extraction complicated by prolonged oozing for 48 hours. She has no family history of known bleeding disorders, though her mother also reports heavy menses. Vital signs are within normal limits, and physical examination reveals scattered ecchymoses on her extremities. To evaluate for von Willebrand disease and determine its specific subtype, arrange the following laboratory investigations in the most appropriate, evidence-based diagnostic sequence.

  1. 1Complete blood count, prothrombin time (PT), and activated partial thromboplastin time (aPTT)
  2. 2Initial specific panel: von Willebrand factor (vWF) antigen, ristocetin cofactor activity, and factor VIII activity
  3. 3Specialized qualitative assay: von Willebrand factor multimer distribution analysis
  4. 4Targeted molecular evaluation: Genetic sequencing of the VWF gene

Cevap

The correct sequence begins with broad hemostatic screening (complete blood count, PT, aPTT), followed by the primary von Willebrand disease diagnostic panel (vWF antigen, ristocetin cofactor activity, and Factor VIII), then specialized functional subtyping via multimer analysis, and finally genetic sequencing if necessary.
The diagnostic approach to von Willebrand disease follows a structured, step-wise algorithm to ensure accuracy and cost-effectiveness. It begins with broad screening (CBC, PT, aPTT) to rule out primary platelet disorders and severe secondary hemostatic defects. Once basic screening points toward vWD or fails to identify a cause despite high clinical suspicion, a primary specific panel (vWF antigen, ristocetin cofactor activity, and Factor VIII) is ordered. If this primary panel indicates a qualitative defect, the third step is multimer analysis to accurately subtype the disease, which impacts management (e.g., DDAVP response). Finally, genetic sequencing is a tertiary test reserved only for complex cases requiring differentiation of specific structural variants or for genetic counseling.

Adım Adım Çözüm

1
Perform initial hemostatic screening with CBC, PT, and aPTT.
Evaluates for basic underlying causes like thrombocytopenia and major intrinsic or extrinsic coagulation factor deficiencies.
This is the cost-effective, essential first step in any bleeding workup to rule out common etiologies before proceeding to specialized, expensive disease-specific panels.
2
Order the initial von Willebrand disease panel (vWF antigen, vWF activity, and Factor VIII activity).
Establishes the diagnosis of von Willebrand disease and provides initial phenotypic categorization into quantitative versus qualitative defects.
Required to confirm the presence of vWF deficiency or dysfunction and to evaluate its secondary effect on Factor VIII stability.
3
Perform von Willebrand factor multimer distribution analysis.
Differentiates between specific qualitative Type 2 vWD subtypes.
This assay is indicated when the initial vWD panel reveals a qualitative defect (e.g., disproportionately low ristocetin cofactor activity compared to antigen levels), as specific subtypes like 2A, 2B, and 2M have different multimer patterns.
4
Consider targeted genetic sequencing of the VWF gene.
Identifies specific causal molecular mutations.
Reserved for specific challenging diagnostic scenarios that cannot be resolved phenotypically, such as differentiating Type 2N vWD from mild Hemophilia A, or for family planning purposes in severe Type 3 disease.

Anahtar Kavram

The laboratory evaluation of a suspected bleeding disorder follows a tiered, cost-effective algorithm: general hemostatic screening precedes specific phenotypic factor assays, which in turn precede complex qualitative multimer analysis and highly specialized molecular genetic testing.
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Ordering Laboratory Tests

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