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Zorluk: OrtaHematology and Oncology

A 48-year-old woman with a history of severe rheumatoid arthritis presents to the clinic with large, unexplained ecchymoses on her thighs and arms over the past two weeks. She has no prior personal or family history of bleeding disorders. Initial laboratory testing reveals an isolated, significantly prolonged activated partial thromboplastin time (aPTT) with a normal prothrombin time (PT) and normal platelet count. Arrange the following steps in the standard diagnostic algorithm used to definitively diagnose an acquired coagulation factor inhibitor in this patient in the correct chronological sequence.

  1. 1Identify an isolated prolonged aPTT on the initial coagulation panel
  2. 2Perform a 1:1 mixing study using the patient's plasma and normal plasma
  3. 3Observe failure of the aPTT to correct, confirming the presence of an inhibitor
  4. 4Perform specific coagulation factor activity assays
  5. 5Quantify the specific autoantibody titer using the Bethesda assay

Cevap

The correct sequence is: Identify isolated prolonged aPTT -> Perform 1:1 mixing study -> Observe failure to correct -> Perform specific factor activity assays -> Quantify titer using Bethesda assay.
The correct sequence logically follows the clinical algorithm for evaluating an isolated prolonged aPTT in a bleeding patient. It starts with the initial screening test, uses a mixing study to categorize the etiology (inhibitor vs. deficiency), identifies the specific factor involved via activity assays, and finally quantifies the disease severity using a specialized test (Bethesda assay).

Adım Adım Çözüm

1
Recognize the initial screening laboratory abnormality.
The patient has an isolated prolonged aPTT.
This isolates the defect to the intrinsic or common pathway, prompting further specific investigation.
2
Determine if the prolongation is due to a factor deficiency or an inhibitor.
A 1:1 mixing study is performed.
Mixing the patient's plasma with normal plasma will correct a deficiency (as normal plasma provides the missing factors) but will not correct an inhibitor (as the autoantibody neutralizes the normal factors).
3
Interpret the mixing study results.
The aPTT fails to correct.
This confirms the presence of a circulating inhibitor (autoantibody), characteristic of acquired hemophilia, rather than a congenital deficiency.
4
Identify the exact target of the inhibitor.
Specific factor activity assays are performed.
It is necessary to know which factor is being inhibited (most commonly Factor VIII in acquired hemophilia A) to confirm the specific diagnosis.
5
Determine the severity and titer of the inhibitor.
A Bethesda assay is conducted.
Quantifying the inhibitor titer is essential to guide therapeutic decisions, such as using bypassing agents (e.g., recombinant Factor VIIa) for high titers versus high-dose factor replacement.

Anahtar Kavram

The diagnostic workup for an unexplained prolonged aPTT involves a stepwise approach: initial identification, mixing study to differentiate deficiency from inhibitor, specific factor assays to identify the target, and finally quantification of the inhibitor titer.
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Hematology and Oncology

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