A 32-year-old woman is evaluated in the clinic for right lower extremity swelling and pain that began two days ago. Venous Doppler ultrasonography confirms an acute deep vein thrombosis in the right popliteal vein. Her past medical history is significant for a spontaneous abortion at 14 weeks gestation two years ago. She takes no medications and has no family history of bleeding or clotting disorders. Physical examination is unremarkable except for moderate right calf swelling and tenderness.
Laboratory results are as follows:
| Laboratory Test | Result | Reference Range |
|---|---|---|
| Hemoglobin | 13.2 g/dL | 12.0-16.0 g/dL |
| Platelet count | 210,000/mm³ | 150,000-400,000/mm³ |
| Prothrombin time (PT) | 12.5 seconds | 11-15 seconds |
| Activated partial thromboplastin time (aPTT) | 62 seconds | 25-40 seconds |
A mixing study with normal pooled plasma is performed. Immediately after mixing, the patient's aPTT is 58 seconds.
Based on these laboratory findings, which of the following is the most likely diagnosis?
- Antiphospholipid syndromeCevap
- BFactor VIII deficiency
- CFactor V Leiden mutation
- DAnti-factor VIII autoantibody
- EVon Willebrand disease
Cevap
Antiphospholipid syndrome
The correct diagnosis is antiphospholipid syndrome. This patient presents with a history of recurrent thrombotic events (deep vein thrombosis and a second-trimester miscarriage). Her laboratory workup reveals an isolated prolonged aPTT. The crucial diagnostic step is the 1:1 mixing study with normal pooled plasma, which fails to correct the aPTT. This failure to correct indicates the presence of a circulating inhibitor in the patient's serum that inhibits the coagulation cascade in the laboratory assay. The lupus anticoagulant is an antiphospholipid antibody that binds to the phospholipids used in the aPTT test, artificially prolonging the result. Despite this in vitro prolongation, lupus anticoagulant is paradoxically prothrombotic in vivo, perfectly matching this patient's clinical presentation.
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Anahtar Kavram
In evaluating an isolated prolonged aPTT, a mixing study differentiates between a factor deficiency (which corrects) and an inhibitor (which does not correct). A non-correcting mixing study in a patient with thrombosis strongly suggests lupus anticoagulant associated with antiphospholipid syndrome.