Heparin cofactor II as a predictor of thrombotic microangiopathy after bone marrow transplantation.

The pathogenesis of thrombotic microangiopathy (TMA) after allogeneic bone marrow transplantation (BMT) remains unclear since ADAMTS13, which is implicated in primary thrombotic thrombocytopenic purpura (TTP), has been shown to have no role in this condition. We investigated whether the onset of TMA after BMT could be predicted by measuring heparin-cofactor II (HC II), a marker for thrombosis of unknown etiology. In 30 consecutive BMT patients, the serum HC II level was measured before conditioning and one week after recovery from leukopenia. Four of the 30 patients developed TMA, and 26 did not. Before conditioning, the mean serum HC II level was 1.748 +/- 0.37 U/mL in the TMA group and 0.889 +/- 0.25 U/mL, in the non-TMA group, being higher in the former group (p < 0.01, t-test). After recovery from leukopenia, the two groups showed no significant difference of serum HC II. The HC II level at the onset of TMA was above the upper limit of normal in only one out of four patients. These results suggest that vascular endothelial damage due to chemotherapy before BMT increases the risk of TMA, and that HC II is useful for predicting the occurrence of TMA after BMT.