Methods for monitoring patients receiving unfractionated heparin (UFH) and Low Molecular Weight heparin (LMWH) anticoagulation therapy will be reviewed. Further, a recent clinical study of data from MedAssets, a healthcare performance improvement company, will be presented and discussed. This study covers a 5-year period, involving a large patient cohort diagnosed with acute coronary syndrome, ischemic stroke or primary venous thromboembolism, receiving Unfractionated Heparin (UFH), and monitored with either Anti-Xa or Activated Partial Thrombin Time (aPTT). Bleeding complications in the two groups are compared. Clinical and economic value of Anti-Xa monitoring and a review of assays for Anti-Xa monitoring will be presented.