Clinical features:
(1) acquired disorder with bruising and bleeding that varies in severity
(2) severe psychiatric disorder (the severity of which may not always be immediately apparent)
(3) denial by the patient even in the face of overwhelming evidence (if the person admits to the intake then the diagnosis is straightforward)
(4) deficiency in vitamin K dependent coagulation factors (Factors II, VII, IX, X) despite documented vitamin K intake or administration
(5) other markers of factitious disease (leaving against medical advice, multiple different doctors, refusal to provide previous medical records, etc.)
Testing blood for the presence of warfarin or superwarfarin (brodifacoum, other) can be diagnostic. Separate assays are required for each class; a negative test for one type does not exclude the other.
Differential diagnosis:
(1) ingestion of coumarin compounds in dietary or herbal supplements (see 04.41)
(2) warfarin therapy prescribed by another physician
(3) severe liver disease
(4) drug that acts as a vitamin K antagonist (phenytoin, aspirin, vitamin E, other)
