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Difficulty: HardDiagnostic Workup and Test Sequencing

Match each patient's clinical presentation and initial coagulation laboratory findings with the most appropriate next step in diagnostic test sequencing.

  • A 34-year-old woman with unprovoked deep vein thrombosis and a history of recurrent miscarriages. Her isolated activated partial thromboplastin time (aPTT) is prolonged and fails to correct with a 1:1 mixing study.Perform dilute Russell viper venom time (dRVVT) and anti-cardiolipin antibody assays.
  • A 65-year-old man with no prior bleeding history presents with sudden, severe muscle hematomas. His isolated aPTT is prolonged and fails to correct with a 1:1 mixing study.Perform coagulation factor VIII activity and inhibitor (Bethesda) assay.
  • A 72-year-old malnourished woman on prolonged broad-spectrum antibiotics presents with large ecchymoses. Both prothrombin time (PT) and aPTT are prolonged but completely correct with a 1:1 mixing study.Administer intravenous vitamin K and repeat coagulation testing.
  • A 22-year-old woman with a lifelong history of epistaxis and heavy menses has normal PT, normal aPTT, and normal platelet count, but prolonged platelet function analyzer (PFA-100) closure time.Measure von Willebrand factor antigen, ristocetin cofactor activity, and factor VIII level.

Answer

Proper evaluation of abnormal coagulation parameters requires interpreting the 1:1 mixing study to differentiate between factor deficiencies (which correct) and inhibitors (which fail to correct), followed by selecting confirmatory tests based on the clinical phenotype of bleeding versus thrombosis.
Test sequencing for complex coagulation disorders strictly follows an algorithmic approach. The 1:1 mixing study is the pivotal branching point. If the mixing study corrects, the etiology is a deficiency (requiring factor assays or replacement trials like Vitamin K). If it fails to correct, an inhibitor is present, and the choice of the confirmatory test depends on whether the patient is experiencing bleeding (requiring a Bethesda assay for acquired hemophilia) or thrombosis (requiring dRVVT for antiphospholipid syndrome).

Step-by-Step Solution

1
Analyze the initial PT and aPTT results to identify the affected coagulation pathway.
Determines whether the defect lies in the intrinsic (aPTT), extrinsic (PT), or common (both) pathways.
This narrows the differential diagnosis to specific factors or inhibitors affecting those pathways.
2
Interpret the results of the 1:1 mixing study using normal plasma.
Correction indicates a factor deficiency; failure to correct indicates the presence of a circulating inhibitor.
Mixing normal plasma replaces missing factors but will be neutralized if an antibody/inhibitor is present.
3
Correlate the laboratory mechanism with the clinical presentation (hemorrhage vs. thrombosis).
Selects the highly specific confirmatory test (e.g., Bethesda assay for bleeding inhibitors, dRVVT for thrombotic inhibitors).
Different inhibitors have opposite clinical manifestations; lupus anticoagulants cause thrombosis in vivo despite prolonging aPTT in vitro.

Key Concept

Diagnostic sequencing of coagulation disorders using the 1:1 mixing study and clinical phenotype.
Estimated Time:2m 0s
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Topics

Diagnostic Workup and Test Sequencing

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