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Difficulty: MediumOrdering Laboratory Tests

A 16-year-old girl is evaluated in the clinic for heavy menstrual bleeding. She reports that since menarche at age 12, her menstrual periods have consistently lasted 8 to 10 days, frequently requiring her to change pads every 2 hours on the heaviest days. She also recalls an episode of prolonged bleeding following a dental extraction two years ago. The patient takes no daily medications, though she occasionally uses ibuprofen for cramps. Family history is notable for a maternal aunt who required a blood transfusion after childbirth. Physical examination reveals normal vital signs, no joint deformities, and no petechiae or ecchymoses. The physician suspects von Willebrand disease (vWD) and plans to initiate a laboratory workup. Arrange the following tiers of laboratory testing in the most appropriate sequential diagnostic order, from initial screening to definitive disease subtyping.

  1. 1Complete blood count, prothrombin time (PT), and activated partial thromboplastin time (aPTT)
  2. 2Plasma von Willebrand factor (vWF) antigen, vWF activity, and Factor VIII coagulant activity
  3. 3von Willebrand factor (vWF) multimer analysis

Answer

The correct sequence of diagnostic testing is: 1) CBC, PT, and aPTT; 2) vWF antigen, vWF activity, and Factor VIII activity; 3) vWF multimer analysis.
The diagnostic evaluation of a suspected bleeding disorder must follow a stepwise, cost-effective algorithmic approach. The correct sequence begins with broad screening tests (CBC, PT, aPTT) to rule out common etiologies like thrombocytopenia. Once basic screening indicates a primary hemostatic defect without thrombocytopenia, the initial specific vWD panel (vWF antigen, vWF activity, and Factor VIII) is ordered to establish the diagnosis. Finally, specialized tests such as vWF multimer analysis are ordered only after confirming the diagnosis in order to determine the specific subtype, which critically dictates whether treatments like desmopressin (DDAVP) will be safe and effective.

Step-by-Step Solution

1
Evaluate the patient's clinical presentation.
The presentation of severe menorrhagia and a history of prolonged bleeding after dental procedures strongly suggests an underlying bleeding diathesis, most likely von Willebrand disease.
Clinical history establishes the pre-test probability and directs the scope of the initial laboratory workup.
2
Determine the most appropriate initial laboratory screening.
Select complete blood count, PT, and aPTT as the first step.
Standard diagnostic algorithms require ruling out common causes of bleeding, such as profound thrombocytopenia or severe global coagulation defects, before ordering expensive specific factor assays.
3
Determine the appropriate confirmatory diagnostic panel.
Select vWF antigen, vWF activity (e.g., Ristocetin cofactor), and Factor VIII activity as the second step.
These tests comprise the initial specific vWD screening panel. They confirm the presence of von Willebrand disease and measure the quantitative or qualitative functional deficiency of the factors.
4
Select the specific subtyping test.
Select vWF multimer analysis as the final step.
Once the diagnosis is confirmed, multimer analysis differentiates the specific disease subtype (e.g., distinguishing Type 1 from Type 2 variants). This is essential because treatments like desmopressin (DDAVP) are effective in Type 1 but can be ineffective or contraindicated in certain Type 2 subtypes.

Key Concept

Stepwise diagnostic evaluation of von Willebrand disease
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Topics

Ordering Laboratory Tests

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