• lupus anticoagulant;
  • acquired factor X deficiency;
  • bleeding disorder/bleeding diathesis;
  • respiratory infection

Summary. Acquired factor X (FX) deficiency is rare, but has been reported in diverse disease states, including systemic amyloidosis and respiratory infections. FX deficiency associated with lupus anticoagulant (LA) and a bleeding diathesis has not been previously reported. We report two patients both of whom presented with a severe bleeding diathesis after a preceding respiratory infection due to isolated FX deficiency associated with a LA. The FX deficiency and LA were transient. We conclude that patients with LA may rarely present with severe acquired FX deficiency. This may be another mechanism whereby patients with antiphospholipid antibodies present with bleeding complications.