A Diagnostic Challenge: Occurrence of Acquired Haemophilia A in Two Patients on Warfarin Therapy

Abstract number: P1401

Riddell A, Brooks S, Unadkat S, Brown SA, Lee CA

We present the clinical and laboratory findings of two patients who developed Acquired Haemophilia A whilst on warfarin therapy.

Case 1:  A 73-year-old female was admitted with multiple DVTs and PEs. The patient was commenced on warfarin therapy and discharged. Readmission because of a large retroperitoneal haematoma and moderate bruising occurred 30 days later (Hb 4.5 g/dL, INR 4.9 and APTT 127 s). Following further massive peritoneal haemorrhage the patient was admitted to ITU (INR 1.7, APTT 113 s). Warfarin therapy was discontinued, and despite the continued use of blood products the peritoneal bleeding continued and the APTT remained prolonged at 65 s. Further laboratory investigations showed an APTT 50/50 mix (50/39), TT (14 s), FVIII:C of 11 IU/dL (50–150 IU/dL) and the FVIII inhibitor titre was 2BU (<0.6BU) increasing to 86 BU the following week. Patient was treated with steroids, IV IgG and FEIBA.

Case 2:  A 69-year-old female (on warfarin treatment) with a severe medical history of systemic sclerosis, pulmonary hypertension and chronic vasculitis with vascular insufficiency was admitted for ulcer management. Whilst in hospital, ampicillin was prescribed for sepsis. During this period it was noted the APTT was disproportionately elevated to 93 s when the INR was 4.3. An APTT 50/50 mix was performed that showed poor correction (45/31). The results of further laboratory investigations were TT (14 s), FVIII:C of 9 IU/dL (50–150 IU/dL) and a FVIII inhibitor level of 1.4 BU (<0.6BU). The FVIII:C level and FVIII inhibitor level remained unchanged with no bleeding symptoms over the following month. Warfarin therapy was discontinued. No treatment was initiated for the inhibitor but the patient was closely monitored.

Conclusion:  In patients treated with warfarin, acquired FVIII inhibitors may be masked. In cases of unresolved bleeding that does not respond to treatment, an APTT, APTT 50/50 mix and TT should be performed followed by investigations for clotting factor inhibitors as required.