title: Optimal Timing for Hemoglobin Concentration Determination after Total Knee Arthroplasty: Day 1 versus Day 2.
abstract: OBJECTIVE
  Postoperative hemoglobin (Hb) determination remains an essential parameter for quantifying blood loss following total knee replacement (TKR) surgery and guiding transfusion practice. In this study we aimed to ascertain the optimal timing for Hb determination postoperatively and assess its relationship to serum hematocrit (Hct).
  
  
  METHODS
  This was a retrospective cohort analysis of 61 consecutive patients undergoing preoperative, day 1 and day 2 Hb and Hct concentration determination following TKR surgery. This was a single centre study in the United Kingdom.
  
  
  RESULTS
  The mean fall in Hb concentration at day 1 was 2.9 g/dL in comparison to 3.3 g/dL at day 2. This indicated a significant difference of 0.39 g/dL (p=0.023). A total of 5 patients required blood transfusions following day 2 Hb determination. Postoperative Hct values varied in close relation with the Hb concentration with no significant differences demonstrated. Our study reveals a significant change between day 1 and day 2 Hb concentrations following TKR surgery, with no significant differing information provided through Hct determination.
  
  
  CONCLUSIONS
  Our results support the use of delayed routine testing at day 2 following surgery as it is likely to more accurately reflect ongoing hidden blood loss into the joint cavity and within soft tissue planes.
authors.affiliation: Department of Trauma and Orthopaedics, Salford Royal NHS Foundation Trust, Salford, UK.
authors.forename: Mahdi Yacine
authors.initials: MY
authors.lastname: Khalfaoui
authors.affiliation: Department of Trauma and Orthopaedics, King's College Hospital, London, UK.
authors.forename: Charles
authors.initials: C
authors.lastname: Godavitarne
authors.affiliation: Department of Trauma and Orthopaedics, King's College Hospital, London, UK.
authors.forename: Michael C P
authors.initials: MC
authors.lastname: Wilkinson
keywords: Arthroplasty; Blood loss; Hematocrit; Hemoglobin; Knee