Blood loss in primary total hip arthroplasty occurs mainly postoperatively, but current formulas for calculating blood loss are inaccurate: a retrospective study of 208 cases.

Introduction Total hip arthroplasty (THA) is potentially associated with high blood loss, possibly requiring transfusion. To avoid well-known complications of allogenic transfusions, risk stratification and patient optimization are recommended. This study explores whether bone quality, as evaluated by the Singh Index (SI), impacts blood loss in primary THA, as recently identified in fracture surgery.Methods Retrospective, single-center study conducted to examine intraoperative blood loss (IBL) and total blood loss (TBL) in primary THA performed in adults through an anterior approach between 10/2021 and 05/2022. TBL estimation utilized formulas of Gross, Camarasa, Frankfurt and OSTHEO.Results A total of 218 unilateral THA were included. TBL substantially exceeded IBL, primarily occurring within the first postoperative day. The formulas were largely consistent, TBL reaching approximately one-third of the estimated total blood volume, except for the Frankfurt formula, which provided much lower values. However, all four formulas failed when IBL exceeds 1'000 ml, a common threshold in THA. Operation time correlated with increased IBL but not TBL. The body mass index (BMI) appeared to be a risk factor for TBL. The SI had a significant but relatively small influence.Conclusion TBL after THA is relevant, accounting for approximately one-third of total blood volume, primarily occurring within the first 24 h. Blood counts are recommended on the first postoperative day and should be repeated on the second day in case of clinical suspicion. There is a correlation between bone quality, as evaluated by the SI, and TBL, but the effect is less than for BMI. Considering ease of use and consideration of RBC (re-)transfusion, the formula from Camarasa et al. appears to be the best available. However, the various formulas available for estimation of perioperative TBL fail at blood losses not uncommon in THA. Therefore, there is a need for new instruments to evaluate TBL.