Differential Diagnosis for a Positive Russell Viper Venom Test

The Russell viper venom test (RVVT) is a laboratory test used to detect the presence of lupus anticoagulant, a type of antiphospholipid antibody. This test is particularly useful because lupus anticoagulant can interfere with phospholipid-dependent coagulation tests, leading to prolonged coagulation times. Given the patient's presentation, here is a differential diagnosis organized into categories:

• Single Most Likely Diagnosis

  • C. Lupus anticoagulant: This is the most likely diagnosis because the RVVT is specifically sensitive for detecting lupus anticoagulant. The presence of lupus anticoagulant is indicated by a positive RVVT, and it is a common cause of a prolonged coagulation time in the absence of bleeding.

• Other Likely Diagnoses

  • A. Protein S deficiency: While less directly related to a positive RVVT, protein S deficiency can sometimes cause issues with coagulation tests due to its role as a cofactor for protein C. However, it's less likely to be the primary cause of a positive RVVT.
  • B. Antithrombin deficiency: Similar to protein S deficiency, antithrombin deficiency affects coagulation but is not typically associated with a positive RVVT. It's a consideration in patients with recurrent thrombosis but not the first suspect in this scenario.
  • D. Protein C deficiency: Like protein S and antithrombin deficiencies, protein C deficiency is more related to thrombophilia rather than directly causing a positive RVVT. It's a consideration in patients with a history of thrombotic events.

• Do Not Miss Diagnoses

  • Antiphospholipid syndrome (APS): Although not listed as an option, APS is a critical diagnosis to consider in the context of a positive RVVT. APS can lead to significant morbidity, including recurrent thrombosis and pregnancy complications, despite the patient's history of uncomplicated pregnancies. Missing this diagnosis could have serious implications for the patient's health.

• Rare Diagnoses

  • Other coagulation factor deficiencies or inhibitors: While rare, other factor deficiencies or the presence of inhibitors could potentially affect the RVVT. However, these would be less common causes of a positive test and would typically be associated with significant bleeding histories, which is not indicated in this patient.
  • Factor V Leiden: Though not directly related to RVVT, in the broader context of thrombophilia and coagulation disorders, Factor V Leiden is a consideration. However, it's more commonly associated with resistance to activated protein C rather than a positive RVVT.