BACKGROUND: Improvement of coagulation function by acute normovolemic hemodilution (ANH) is well evidenced in modern medical practice. It has been reported that there are fixed differences in the plasma concentrations of von Willebrand factor and factor VIII according to ABO blood types. Therefore, the changes of coagulation state among ABO blood types during ANH are expected but have not yet been studied. This study was designed to establish the changes of coagulation state among ABO blood types during ANH by intraoperative thrombelastography (TEG). METHODS: Fifty one healthy adult patients scheduled for spine surgery were enrolled in this study. All patients were grouped by ABO blood types and underwent ANH after the induction of general anesthesia. While autologous blood (25% of EBV) was procured, warmed 0.9% saline, 3 times the blood volume deficit, was infused to maintain normovolemia. Platelet count, prothrombin time (PT), activated partial thromboplastin time (APTT), factor VIII activity and TEG were performed to evaluate coagulation state before and after ANH. Statistical analysis was conducted to determine the dilutional effects and intergroup differences. RESULTS: Improvement of coagulation function after ANH was visible only by TEG, and not by PT, APTT or factor VIII activity. Fourteen of fifteen patients with type O blood showed decreased factor VIII activity to under the normal limit after ANH. In patients with blood type O, changes of APTT (P = 0.093, P = 0.086) and factor VIII activity (P = 0.001, P = 0.004) during ANH were remarkable in comparison with blood type B and AB. CONCLUSIONS: ANH enhances coagulation function evaluated by means of TEG. No difference was observed in terms of the changes of coagulation state among ABO blood types during ANH. However, ANH should be instituted cautiously in patients with type O blood because there is a possibility of impairing factor VIII activity.