Description
Objectives: This study aimed to evaluate the diagnostic characteristics of tryptophanyl tRNA synthetase (WRS) for the diagnosis of septic arthritis of the knee joint and to determine whether it is a reliable and sensitive synovial biomarker for discriminating septic arthritis from other types of arthritis.
Methods: Patients with "hot, swollen, joint" presenting in an emergency setting, joint effusions were prospectively recruited between January 2019 and September 2020. Nine patients had septic arthritis, 6 had acute gout attack, 1 had an acute flare of chronic rheumatic arthritis, and 46 had aggravated osteoarthritis or reactive arthropathy. Traditional inflammatory markers were measured, and their diagnostic abilities were compared. Neutrophil count, Creactive protein (CRP) level, WRS, and human neutrophil a-defensin levels were assessed in the synovial fluids. Demographic parameters and biomarkers with a P-value < 0.05 in differentiating septic from non-septic arthritis were included in a multivariable model. A multivariable logistic regression with a stepwise selection was performed to build the final combined model. Receiver operating characteristic curves were used to establish optimal thresholds for the diagnosis of septic arthritis of the knee joint, and the area under the curve was calculated to determine the overall accuracy of these tests compared to non-septic inflammatory arthritis patients.
Results: Septic arthritis patients were more likely to display higher serum WBC and CRP levels, synovial neutrophil counts, and levels of two synovial biomarkers, including WRS and a-defensin. WRS showed the highest specificity (87.5%) and sensitivity (83.3%) with a-defensin among the three synovial biomarkers. In the multivariate model, which included the blood CRP level, synovial fluid α-defensin, and WRS level, WRS was the most discriminating diagnostic biomarker, distinguishing septic arthritis from non-septic inflammatory arthritis with an 88.9% sensitivity, an 88.7% specificity, a 57.1% PPV, and 88.7% NPV. The diagnostic optimal threshold for serum CRP was 18 mg/L for patients with septic inflammatory arthritis. Similarly, the optimal threshold for the synovial fluid WBC count was 81,120/µL for patients with septic inflammatory arthritis. Finally, the optimal thresholds for the synovial fluid biomarkers of WRS and α-defensin were 418 and 301, respectively.
Conclusions: Synovial fluid WRS is a relevant biomarker in discriminating septic arthritis from other inflammatory arthritis and should be tested in an independent cohort
