A 35 yr old lady with normal PT and increased aPTT. 2 year back, she was operated for cholecystectomy & did not have any bleeding episoe. What is next investigation for clinical diagnosis –
## **Core Concept**
The patient presents with a prolonged activated partial thromboplastin time (aPTT) and a history of surgery without bleeding complications. This scenario suggests an isolated prolongation of aPTT, which can be due to various causes including coagulation factor deficiencies, the presence of inhibitors, or lupus anticoagulant.
## **Why the Correct Answer is Right**
The correct approach to diagnose the cause of isolated aPTT prolongation involves mixing studies and further specific tests. A mixing study is performed by mixing the patient's plasma with normal plasma in a 1:1 ratio and then retesting the aPTT. If the aPTT normalizes, it suggests a deficiency of a coagulation factor. If the aPTT remains prolonged, it indicates the presence of an inhibitor. Given the patient's history of surgery without bleeding and the isolated prolongation of aPTT, the next logical step would be to perform a **mixing study** to differentiate between a factor deficiency and an inhibitor.
## **Why Each Wrong Option is Incorrect**
- **Option A:** Although specific tests for factor deficiencies (like Factor VIII, IX, XI, XII) are crucial, they are not the immediate next step without first performing a mixing study to guide which factor to test.
- **Option B:** Directly testing for **Lupus Anticoagulant** could be relevant given its association with aPTT prolongation, but it's not the immediate next step without first confirming the presence of an inhibitor through a mixing study.
- **Option C:** Testing for **Factor VIII levels** might be indicated if the mixing study suggested a factor deficiency, but it's premature without that initial step.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that a mixing study is a critical initial step in the evaluation of isolated aPTT prolongation. It helps differentiate between factor deficiencies (which correct with mixing) and inhibitors (which do not correct). This step is crucial for guiding further testing and management.
## **Correct Answer:** B. Mixing study.