Anesthesiologists love to measure things. Heart rate, blood pressure, and pulse oximetry values all provide information that aids in directing anesthetic care. In fact, these measurements are necessary to provide a safe anesthetic. Laboratory measurements also play a role in guiding therapy, albeit without the instant gratification of vital sign changes. For example, most practitioners would feel uncomfortable administering insulin to a patient without the ability to measure a blood glucose level at some point. Transfusion of blood products is a more complex issue, but one that also relies heavily on measurement-or at least it should. The use of viscoelastic hemostatic testing (VHT) in surgical patients has exploded over the past decade, in part because of its ability to simultaneously measure several components of coagulation. No less than a half dozen different perioperative Societies have published guidelines recommending its use for directing the transfusion of hemostatic blood products. 1-4 Yet, questions still remain about the efficacy of this testing modality, including how we act upon the information it provides. In this issue of the Journal, Lodewyks et al. present a systematic review and meta-analysis of VHT in cardiac surgical patients. 5 Using 11 different randomized-controlled trials involving over 8,000 patients, the authors found no reduction in the proportion of patients exposed to allogenic blood products. They conclude that ''the benefits associated with viscoelastic testing in cardiac surgery patients are insufficiently robust to recommend routine 123