An individual scheduled for an elective herniorrhaphy undergoes a routine preoperative evaluation. The patient notes a lifelong history of prominent bruising and extended bleeding following minor dental procedures. Initial laboratory screening reveals a normal prothrombin time (PT), an unremarkable platelet count, and a markedly prolonged activated partial thromboplastin time (aPTT). There is no history of anticoagulant medication use. Which of the following is the most appropriate next step in laboratory evaluation?
- Perform a 1:1 mixing study with normal plasmaCevap
- BOrder specific factor VIII, IX, and XI activity levels
- CMeasure antiphospholipid antibodies including lupus anticoagulant
- DRequest a comprehensive platelet aggregation study
- EOrder a venous duplex ultrasound of the lower extremities
Cevap
Perform a 1:1 mixing study with normal plasma
The correct action is to perform a 1:1 mixing study. When a patient presents with an isolated prolongation of the activated partial thromboplastin time (aPTT), the foundational next step is to differentiate between a coagulation factor deficiency (such as Factor VIII, IX, or XI) and the presence of an inhibitor (such as a specific factor inhibitor or lupus anticoagulant). Adding normal plasma to the patient's plasma will correct the aPTT if there is a deficiency, as the normal plasma provides the missing factors. If an inhibitor is present, it will neutralize the factors in the normal plasma, and the aPTT will remain prolonged. This step correctly sequences the diagnostic workup before more costly and specific assays are ordered.
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Anahtar Kavram
The initial evaluation of an isolated prolonged aPTT requires a 1:1 mixing study to differentiate between a coagulation factor deficiency and an acquired inhibitor.