Synovial-to-blood glucose ratio as a biomarker for the early diagnosis of septic arthritis of the knee in emergency medical practice: a retrospective clinical cohort study

This study aimed to analyze both hematological and synovial biomarkers in patients with septic arthritis (SA) and patients with non-septic arthritis (non-SA) of the knee and identify useful biomarkers for the early diagnosis of SA in emergency medical practice. We examined 397 knee joints of 367 patients with painful/swollen knee joints and potential infection at our department between May 2018 and May 2023. After excluding cases involving joints with prosthetic replacements, symptom duration more than 3 weeks, prior antibiotic use, and absence of arthrocentesis, 179 knee joints (166 patients) were assessed. To identify useful diagnostic parameters of the SA and non-SA groups, we compared their hematological and synovial fluid biomarkers and assessed the diagnostic performance of those biomarkers by conducting receiver-operating characteristic (ROC) analyses. Hematological parameters, including the white blood cell (WBC) count, neutrophil sequestration, C-reactive protein level, and procalcitonin level, in the SA group were higher than those in the non-SA group. A synovial fluid examination revealed that the WBC count and neutrophil sequestration exhibited the same pattern. Synovial glucose levels and synovial-to-blood glucose ratios in the SA group were lower than those in the non-SA group. The ROC analysis revealed that the synovial-to-blood glucose ratio had the highest diagnostic utility for predicting SA. The synovial-to-blood glucose ratio appears to be a promising biomarker; however, its ability to differentiate SA from non-SA warrants further validation. The synovial-to-blood glucose ratio may complement existing diagnostic tools and improve early diagnostic precision in emergency medical settings.