We read with interest the large study on the use of tranexamic acid (TA) in 414 consecutive patients undergoing total knee arthroplasty (TKA) published by Lozano et al . in Vox Sanguinis [1]. The authors showed that the routine use of TA administration in the management of TKA was associated with significant reduction in allogeneic blood transfusion (ABT) rate and blood management costs [1]. More importantly, this study, which encompassed the largest number of patients reported so far, showed that TA did not seem to be associated with an increased rate of thromboembolic complications [6/215 (2·4%) vs. 3/199 (1·5%), for control and TA groups, respectively; P = 0·507]. We would like, however, to comment regarding data of efficacy and costs. First, the ABT rate in the control group (54%) is significantly higher than that observed in two recent series of TKA patients with similar age, gender distribution and preoperative haemoglobin (30%), and the same is true for patients receiving TA when compared to those receiving postoperative unwashed shed blood (USB, 0·78 ± 0·52 units per patient) or preoperative treatment with oral iron [2,3] (Table 1). One possible reason for these differences may the use of high vacuum drains (650 mmHg), which resulted in a higher estimated blood loss (2325 ± 1196 ml and 1592 ± 823 ml, for control and TA, respectively) [1], when compared to a similar study using low vacuum drains (100 mmHg; 1744 ± 804 ml and 1301 ± 621 ml, respectively) [4]. In this later study, the use of low vacuum drains with reinfusion resulted in an ABT rate of 12·2% (6/49), which was decreased to 2·2% (1/46) by its combination with TA [4]. Second, in their economical analysis, the official price of a red blood cell (RBC) unit in Catalonia, Spain ( a 97·63), was used [1]. However, this so-called ‘official price’ is indeed a ‘political price’ for blood interchange between autonomic communities within Spain, and it does not correspond to the actual production costs of a RBC unit. In addition, the costs of pre-transfusion tests and giving set were also not included. Therefore, in agreement with average cost within the European Union, we estimated an actual cost of a 320 for one RBC transfusion in Spain [5]. Using this figure, the use of TA in TKA reduced transfusion cost per patient to a 108 (Table 1), which favourably compared to the cost of a 177 per patient for USB return ( a 120 per USB collection device) [2], but not with that of preoperative oral iron plus restrictive transfusion protocol ( a 46 per patient) [3]. All together, these results