Diagnostic Value of the Neutrophil-Lymphocyte Ratio in Fracture-Related Infections: A Retrospective Analysis.

Objectives: To determine whether the previously established neutrophil-to-lymphocyte ratio (NLR) threshold of 2.45 accurately diagnoses fracture-related infection (FRI).

Methods: Design: Retrospective diagnostic study.

Setting: Single Level I trauma center.

Patient selection criteria: Included were consecutive adults (≥18 y) who underwent deep-tissue or bone biopsy for suspected FRI between January 1, 2018, and December 31, 2024; excluded were patients with immunosuppressive and oncological disorders or missing laboratory data.

Outcome measures and comparisons: Primary outcome was diagnostic accuracy of NLR-reported as sensitivity, specificity, and area under the receiver-operating-characteristic (ROC) curve-for fracture-related-infection. Neutrophil-lymphocyte-ratios of patients with confirmed fracture-related-infection confirmed via bone or deep tissue biopsy were compared with those of patient's with negative (aseptic) biopsies. Per AO/ASIF consensus criteria, biopsy results were considered positive for infection if: (1) phenotypically indistinguishable pathogens were identified by culture from at least two separate deep tissue/implant specimens, or (2) the presence of microorganisms in deep tissue specimens confirmed by histopathological examination.

Results: Forty biopsies from 29 patients met inclusion criteria. Of the 40 biopsies, 27 were septic and 13 aseptic. The septic cohort had a mean age of 44 years with a range of 18-64 and consisted of 20 males and 2 females. The aseptic cohort had a mean age of 49 with a range of 27-70 and consisted of 6 males and 1 female. Using the pre-specified NLR threshold of 2.45, sensitivity and specificity for diagnosing fracture-related infection were 92.6% (95% CI 75.7-99.1) and 92.3% (95% CI 64.0-99.8), respectively. Exploratory Receiver operating characteristic analysis suggested an optimal NLR cut-off point of 2.52 for detecting FRI, with an area-under-the-curve of 0.89 (95 % CI 0.74-1.00). Median NLR was significantly higher in septic biopsies, 4.79 (IQR 3.95-8.54), than in aseptic biopsies, 1.78 (IQR 1.50-2.15) (p = 0.003). An NLR > 2.45 occurred in 92.6 % of septic versus 7.7 % of aseptic biopsies (p < 0.001; OR 150, 95 % CI 12.4-1822.3).

Conclusions: An NLR threshold of 2.45 provided high sensitivity and specificity for detecting fracture-related infection. These findings support its potential utility as a non-invasive screening tool to detect fracture-related infections.

Level of evidence: III.