Shape of the association between preoperative hemoglobin level and postoperative outcomes in patients undergoing primary arthroplasty

BACKGROUND: The shape of the association between preoperative hemoglobin level and outcomes after primary arthroplasty has not been adequately described. This study aimed to characterize the association between preoperative hemoglobin level and important outcomes after primary hip and knee arthroplasty and how this association is influenced by other key confounders. METHODS: Using de-identified, population-based health administrative data for Ontario housed at ICES, we identified all primary hip and knee arthroplasty procedures performed in Ontario between April 2007 and March 2017. Preoperative hemoglobin level, age, sex, Charlson Comorbidity Index score, American Society of Anesthesiologists score, preadmission living status, Hospital-patient One-year Mortality Risk (HOMR) score, and serum sodium and creatinine levels were extracted. All relevant postoperative outcomes that could be measured accurately were identified. We performed multivariable logistic regression and restricted cubic splines analyses. RESULTS: A total of 188 176 patients clustered within 532 surgeons were studied. The adjusted likelihood of transfusion increased notably and progressively when the preoperative hemoglobin level was below 135 g/L; duration of surgery, patient age and HOMR score amplified this association. Risk of postoperative admission to critical care showed a linear association with preoperative hemoglobin level. Risks of unplanned 30-day emergency department visit, 30-day readmission and 1-year all-cause mortality showed curvilinear associations with baseline hemoglobin level, with risks being notably greater as the level deviated from 137 g/L to 141 g/L. CONCLUSION: Preoperative hemoglobin levels, both high and low, were independently significantly associated with primary arthroplasty outcomes, and levels at which outcome risks started to increase exceeded threshold values commonly used to define "normal." Preoperative hemoglobin level should be considered in future bundled payment models that aim to account for case-mix when grading postarthroplasty outcomes.