Revisiting INR Targets Prior to TKA

An elevated International Normalized Ratio (INR)—a standardized gauge for how long it takes blood to clot—is rarely a good sign when someone is about to undergo an elective orthopaedic procedure. This is especially true for larger surgeries such as total hip or knee arthroplasty, in which there are already concerns about perioperative bleeding. Excessive surgery-related blood loss can lead to wound complications, increased length of hospital stay, and higher mortality rates. But what precisely constitutes an “elevated” INR? While some recommendations suggest that elective procedures be performed only when a patient’s INR is ≤1.5, the evidence supporting this recommendation, especially in the setting of total knee arthroplasty (TKA), is sparse at best.

In the March 20, 2019 issue of The Journal, Rudasill et al. use the National Surgical Quality Improvement Program (NSQIP) database to help define what “elevated” should mean in the context of TKA. They evaluated data from >21,000 patients who underwent a TKA between 2010 and 2016 and who also had an INR level reported within one day before their joint replacement. They stratified these patients based on their INR levels (≤1, >1 to 1.25, >1.25 to 1.5, and >1.5). Using multivariate regression analysis to adjust for patient demographics and comorbidities, the authors found a progressively increasing risk of bleeding requiring transfusion for each group with an INR >1 (odds ratios of 1.19, 1.29 and 2.02, respectively).  Relative to patients with an INR of ≤1, Rudasill et al. also found a significantly increased risk of infection in TKA patients with an INR >1.5 (odds ratio 5.34), and an increased risk of mortality within 30 days of surgery among patients with an INR >1.25 to 1.5 (odds ratio 3.37). Lastly, rates of readmission and the length of stay were significantly increased in patients with an INR >1.25.

While there are certainly weaknesses inherent in using the NSQIP dataset, this study is the first to carefully evaluate the impact of slight INR elevations on post-TKA morbidity and mortality. While I was not surprised that increasing INR levels were associated with increased bleeding events, I was impressed by the profound differences in length of stay, infection, and mortality between patients with an INR ≤1 and those with an INR >1.25. I agree with the authors’ conclusion that “current guidelines for a target INR of <1.5 should be reconsidered for patients undergoing TKA.”  Further, based on the risks highlighted in this study, prospective or propensity matched cohort studies should be performed to help determine whether anyone with an INR >1 should undergo a TKA.

Chad A. Krueger, MD
JBJS Deputy Editor for Social Media

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One response to “Revisiting INR Targets Prior to TKA”

  1. Shyan Goh says :

    Another day, another study which raises more questions than answers.

    But what questions?

    This study may purport to address the relationship of preop INR and outcome of primary TKR and *perhaps* it did suggest that INR > 1.25 was associated with increased bleeding, infection, and mortality rates.

    But who are these “patients for whom an INR had been recorded within 1 day before the TKA and were included for analysis in the present study”? These patient account for 9.6% of all TKA in the database. Why was INR performed in less than 24 hrs of a major surgery? Was it because of the warfarin they were taking? Was it concerns of malnutrition, particularly in Vit K? Perhaps someone discovered liver dysfunction and was doing the test to exclude hepatic failure?

    Did the patient require a change of anesthetic technique to accommodate the higher INR? How about that mortality from GA rather than spinal or regional block?

    So many questions to influence outcome, which severely limits the conclusion of this retrospective paper.

    Like

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