Protein C and S levels in acute leukemia

Patients with acute leukemia undergoing remission induction chemotherapy occasionally develop venous thrombosis despite severe thrombocytopenia and in the absence of disseminated intravascular coagulation. This observation prompted us to study the levels of the naturally occurring anticoagulant proteins C and S prospectively in patients undergoing remission induction chemotherapy for acute leukemia. Plasma samples from 50 adult patients with acute leukemia (34 AML, 16 ALL) were analyzed for protein C antigen, functional protein C, immunologic total and free protein S as well as levels of C4b binding protein (C4bBP). Plasma levels of immunologic protein C were significantly lower in patients with active acute myelocytic leukemia (mean = 77.9) than in controls (mean = 123.6) or patients in remission (mean = 132). Functional protein C levels were also significantly lower in AML patients with active disease (mean = 58.5) than controls (mean = 95.5) or patients in remission (mean = 98.5). Patients with acute lymphocytic leukemia (ALL) had normal levels of immunologic and functional protein C. Although total protein S levels were normal in all patients studied, levels of free protein S were significantly decreased in patients with active AML (mean = 29.3) compared with patients in remission (mean = 42.0) or controls (mean = 42.4). In contrast, patients with ALL, both with active disease and in remission had normal free protein S levels. This decrease in free protein S seen in active AML was not associated with liver disease, white cell count or an increase in C4bBP. These findings provide a possible explanation for the occasional occurrence of venous thrombosis in patients with acute myelocytic leukemia.