For patients with severe obesity undergoing knee or hip replacement, commonly obtained laboratory values - including markers of anaemia and inflammation - are independent predictors of the risk of periprosthetic joint infection (PJI), according to a study by researchers from the Keck School of Medicine of the University of Southern California, Los Angeles.
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. Dr Nathanael D Heckmann, and 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 laboratory values relevant to proposed mechanisms of increased PJI risk associated with morbid obesity.
Several laboratory 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 haemoglobin levels indicating anaemia and in 2.14% of patients with abnormal (high or low) platelet counts.
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 laboratory markers were independently associated with PJI risk. Odds ratios were 2.62 for haemoglobin, 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 haemoglobin 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 anaemia and PJI is even stronger among patients with severe obesity, compared with the general population.
However, more research will be needed to confirm the impact of preoperative platelet count and complete blood count–based ratios on PJI risk.
"This heightened risk signifies the critical importance of identifying anaemia in morbidly obese patients to effectively assess PJI risk prior to TJA," the researchers concluded. "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."
The findings were reported in the paper, ‘Preoperative Laboratory Values Predicting Periprosthetic Joint Infection in Morbidly Obese Patients Undergoing Total Hip or Knee Arthroplasty’, published in the Journal of Bone and Joint Surgery.
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