A 66-year-old woman suffering from fever and thrombophlebitis was refe
rred to our hospital. A peripheral blood examination revealed hyperleu
kocytosis with 96% blast cells and thrombocytopenia. The patient was d
iagnosed as having acute myeloid leukemia (AML) accompanied by dissemi
nated intravascular coagulation (DIC). A marked decrease in protein C
(PC) antigen and activity were observed. In this case, PC levels were
lower than those observed in AML with DIC. Induction therapy for leuke
mia and treatment of DIC were started on the first day of hospitalizat
ion. The patient achieved complete remission, with PC antigen and acti
vity levels normalized.