Differential Diagnosis for Prolonged aPTT

The patient's laboratory results show a prolonged activated partial thromboplastin time (aPTT) with a mixing study that does not correct immediately or after incubation, suggesting an inhibitor rather than a factor deficiency. Given the clinical context and laboratory findings, the differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis

  • C. lupus anticoagulant: This is the most likely diagnosis because the patient has a prolonged aPTT that does not correct with mixing studies, which is characteristic of the presence of an antiphospholipid antibody, such as lupus anticoagulant. Lupus anticoagulant is known to cause a prolonged aPTT due to its interference with the coagulation cascade, particularly in the phospholipid-dependent steps. The lack of bleeding symptoms is also consistent with lupus anticoagulant, as it is more commonly associated with thrombotic events rather than bleeding.

• Other Likely Diagnoses

  • D. specific factor VIII inhibitor: Although less common, a specific factor VIII inhibitor could also cause a prolonged aPTT. However, this condition is typically associated with significant bleeding symptoms, which the patient denies. The mixing study results could support this diagnosis if the aPTT normalizes after the confirmatory assay, indicating the presence of an inhibitor that can be overcome by adding more factor VIII.
  • B. DIC (Disseminated Intravascular Coagulation): While DIC can cause a prolonged aPTT, it is usually associated with other abnormalities such as thrombocytopenia, prolonged prothrombin time, and elevated fibrin degradation products. The patient's platelet count and prothrombin time are within normal limits, making DIC less likely.

• Do Not Miss Diagnoses

  • A. hereditary factor VIII deficiency (Hemophilia A): Although the patient is female and thus less likely to have hemophilia A (which is X-linked recessive), carriers can occasionally exhibit mild symptoms due to lyonization (X-chromosome inactivation). However, the lack of bleeding symptoms and the specific laboratory findings make this diagnosis less likely. It's crucial not to miss this diagnosis due to its significant implications for bleeding risk, especially in a surgical context.

• Rare Diagnoses

  • Other rare coagulation factor inhibitors (e.g., factor IX, XI, XII inhibitors) could also present with a prolonged aPTT. However, these are exceedingly rare and would be considered only after more common causes have been ruled out.
  • Acquired coagulation factor deficiencies due to other causes (e.g., liver disease, vitamin K deficiency) could also lead to a prolonged aPTT but would typically be associated with other laboratory abnormalities and clinical findings.