Acquired factor V inhibitor in a patient with a mechanical aortic valve under warfarin therapy

Area of Science:

• Hematology
• Immunology
• Pharmacology

Background:

• Warfarin therapy requires careful monitoring due to its narrow therapeutic index.
• Mechanical heart valve replacement is a common surgical procedure.
• Antibiotic treatment can sometimes interfere with coagulation pathways.

Observation:

• An 84-year-old woman on warfarin presented with significant coagulation abnormalities (prolonged PT and APTT, low factor V activity) after antibiotic treatment for pyelonephritis.
• Despite no overt bleeding, a factor V inhibitor was detected.
• The patient had a history of mechanical valve replacement involving bovine thrombin.

Findings:

• The patient's coagulation abnormalities rapidly normalized after initiating prednisolone treatment.
• The presence of a factor V inhibitor was confirmed, likely triggered by bovine thrombin exposure during surgery.
• Low factor V activity (4%) and a high inhibitor level (8 BU) were key laboratory findings.

Implications:

• Factor V inhibitors should be considered in the differential diagnosis of unexpected International Normalized Ratio (INR) prolongation in patients on warfarin, especially post-surgery.
• Bovine thrombin exposure during cardiac surgery is a potential cause of acquired factor V inhibitors.
• Prompt diagnosis and treatment with corticosteroids can effectively manage acquired factor V inhibitors.