Revisiting the International Normalized Ratio Threshold for Bleeding Risk and Mortality in Primary Total Hip Arthroplasty

Background: Efforts to identify preoperative risk factors for primary total hip arthroplasty have amplified with its increasing incidence. The international normalized ratio (INR) is 1 measure that may influence postoperative outcomes. This study of a national database assessed whether there exists an association between preoperative INR and postoperative bleeding and mortality among patients who underwent primary total hip arthroplasty.

Methods: We retrospectively analyzed 17,567 adult patients who underwent primary total hip arthroplasty in the American College of Surgeons National Surgical Quality Improvement Program (NSQIP) between 2005 and 2016. Patients were stratified by preoperative INR into 4 groups: INR <1.0, 1.0 to <1.25, 1.25 to <1.5, and ≥1.5. Bleeding necessitating transfusion was the primary outcome, and secondary outcomes included mortality, infection, and readmission. Multivariable logistic regressions controlled for baseline differences.

Results: Among the patients who underwent total hip arthroplasty, 20.5% had INR <1.0, 73.6% had INR 1.0 to <1.25, 4.2% had INR 1.25 to <1.5, and 1.8% had INR ≥1.5. Mortality increased incrementally from 0.3% for INR <1.0 to 4.9% for INR ≥1.5 (p < 0.001), and bleeding risk increased from 13.2% for INR <1.0 to 29.3% for INR ≥1.5 (p < 0.001). After adjustment, bleeding risk was increased for INR 1.25 to <1.5 (odds ratio [OR], 1.55 [95% confidence interval (CI), 1.26 to 1.92]) and INR ≥1.5 (OR, 1.55 [95% CI, 1.15 to 2.08]) compared with INR <1.0. The only group associated with increased mortality was INR ≥1.5 (OR, 2.69 [95% CI, 1.07 to 6.76]). The length of stay significantly increased with increasing INR, from 3.6 to 6.3 days (p < 0.001).

Conclusions: This study found a significant, independent effect between increased preoperative INR and increased bleeding and mortality. Bleeding risk becomes evident at INR ≥1.25, and those patients with INR ≥1.5 are at significantly increased risk of mortality.

Level of Evidence: Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.