TNXA and hereditary antithrombin deficiency: We also found that the value of APTT in monitoring UFH was no less than the anti-Xa level for the following reasons: (1) In patients without antithrombin deficiency, APTT strong correlation with anti-Xa; (2) in patients with antithrombin deficiency, both APTT and anti-Xa did not correlate well with UFH dose; (3) APTT is common and can be performed several times a day for monitoring UFH.