Summary: Lab values including hemoglobin level, platelet count, and markers of inflammation independently predict the risk of periprosthetic joint infection (PJI) in severely obese patients undergoing knee or hip replacement.

Three Takeaways:

  1. Risk Identification: Elevated hemoglobin levels indicating anemia, abnormal platelet counts, and inflammatory markers like neutrophil-lymphocyte ratio are significantly associated with increased PJI risk in severely obese patients post total joint arthroplasty (TJA).
  2. Clinical Implications: These lab values can potentially aid surgeons in risk-stratifying morbidly obese patients prior to surgery, allowing for targeted interventions to mitigate PJI risk.
  3. Need for Further Study: While these findings are promising, further prospective studies are required to validate the clinical utility of these markers and establish clear guidelines for risk assessment in this high-risk patient population.

For patients with severe obesity undergoing knee or hip replacement, commonly obtained lab valuesincluding markers of anemia and inflammationare independent predictors of the risk of periprosthetic joint infection (PJI), reports a study in TheJournal of Bone & Joint SurgeryThe journal is published in the Lippincott portfolio by Wolters Kluwer. 

Lab values, including: hemoglobin level, platelet count, and several markers of systemic inflammation may be relevant to the elevated rates of PJI following total joint arthroplasty among patients with a body mass index (BMI) of 40 kg/m2 or higher, according to the new research by Nathanael D. Heckmann, MD, and colleagues of Keck School of Medicine of the University of Southern California, Los Angeles. “These findings may help surgeons risk-stratify morbidly obese patients, who represent a growing high-risk TJA population,” the researchers write. 

New Data on Laboratory Predictors of PJI in Morbid Obesity 

An increasing proportion of patients undergoing total hip or knee arthroplasty have morbid obesity. Many studies have found that these patients are at an elevated risk of PJI, up to five times higher than in normal-weight patients. Heckmann and his colleagues sought to identify preoperative laboratory markers associated with an increased risk of PJI among patients with morbid obesity.  

The analysis included 6,780 patients with a BMI of 40 or higher who underwent total knee or hip arthroplasty, as identified with use of data from a national insurance claims database. The analysis focused on lab values relevant to proposed mechanisms of increased PJI risk associated with morbid obesity. 

Several lab values were associated with increased rates of developing PJI within 90 days postoperatively. Compared to an overall rate of 0.69%, PJI developed in 1.69% of patients with hemoglobin levels indicating anemia and in 2.14% of patients with abnormal (high or low) platelet counts.  

Critical Importance of Assessing Lab Values

Elevated levels of certain complete blood count (CBC)–based ratios indicating systemic inflammation were also linked to increased risk of PJI, including 1.11% for an increased neutrophil-lymphocyte ratio, 1.69% for an increased platelet-lymphocyte ratio, and 1.05% for an increased systemic immune-inflammation index. 

After adjusting for potential confounders, all of these preoperative lab values were independently associated with PJI risk. Odds ratios were 2.62 for hemoglobin, 3.50 for platelets, 2.38 for neutrophil-lymphocyte, 4.86 for platelet-lymphocyte ratio, and 2.44 for systemic immune-inflammation index.  

Several comorbid conditions were more common in patients with PJI, including chronic pulmonary disease, complicated diabetes, and complicated hypertension. In contrast with previous reports, albumin and glycated hemoglobin levels were not associated with PJI risk. 

Within the limitations of the retrospective study, the findings help to address the “paucity of data” regarding factors contributing to the elevated risk of PJI associated with morbid obesity. Added to previous studies, the findings suggest that the association between anemia and PJI is even stronger among patients with severe obesity, compared with the general population. “This heightened risk signifies the critical importance of identifying anemia in morbidly obese patients to effectively assess PJI risk prior to TJA,” the researchers write.  

More Research Needed

However, more research will be needed to confirm the impact of preoperative platelet count and complete blood count–based ratios on PJI risk. Heckmann and the coauthors conclude: “Additional prospective studies should be conducted to validate the clinical utility of these laboratory markers to help risk-stratify morbidly obese patients prior to elective TJA.”