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.
CONCLUSIONS: 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.