Changes in perioperative hemoglobin and hematocrit in patients undergoing total knee arthroplasty: a prospective observational study of optimal timing of measurement

OBJECTIVE: This study was performed to depict the patterns of change in the perioperative hemoglobin (Hb) concentration and hematocrit (Hct) and to identify the optimal timing of Hb and Hct measurement in patients undergoing total knee arthroplasty (TKA). METHODS: This prospective observational study involved 302 consecutive patients who underwent TKA. The patients were kept in hospital for 1 full week postoperatively. Hb and Hct measurements were performed preoperatively and on days 1 to 7 postoperatively and then during clinic visits at 1, 3, and 6 months postoperatively. RESULTS: The Hb concentration and Hct decreased during the first few days postoperatively and reached a nadir on postoperative day 4 and 3, respectively; they then recovered in the following days. Significant differences in the Hb concentration and Hct were detected between the preoperative period and day 1, between days 1 and 2, between days 2 and 3, between day 7 and 1 month, and between 1 and 3 months. A significant difference in the Hct was also detected between 3 and 6 months. CONCLUSION: The optimal timing of Hb and Hct measurement is on postoperative day 3 or 4. This timing accurately reflects ongoing hidden blood loss to better guide blood transfusions.