© 2021Introduction: Although early diagnosis of septic arthritis may reduce mortality rates, and limit unnecessary surgical interventions, clinical parameters alone are not adequate for making the diagnosis of septic arthritis. Therefore, relevant laboratory parameters are used to enhance diagnostic sensitivity. The aim of our study was to assist in making the diagnosis of septic arthritis, and prevent delays in the diagnosis. For this purpose; we aimed to determine the diagnostic values of human neutrophil peptides 1-3 (HNP 1-3) and procalcitonin (PCT) in synovial fluids of patients with arthritis. By comparing the HNP 1-3 and procalcitonin levels, as well as CRP, in synovial fluid aspirates, we evaluated the significance of these data in the differential diagnosis of septic arthritis from noninfectious arthritis. Methods: A total of 67 adults consisting of 37 septic arthritis and 30 noninfectious arthritis patients were included in our study. As bioindicators; levels of HNP 1-3, PCT, synovial and serum CRP levels were found to have significant ROC areas in discriminating septic arthritis patients from noninfectious arthritis patients. Results: As a result, synovial fluid HNP 1-3 levels were significantly higher in septic arthritis patients compared to noninfectious arthritis patients (p < 0.001). The sensitivity, specificity, and accuracy of HNP 1-3 levels in the diagnosis of septic and noninfectious arthritis were found as 86%, 87%, and 87%, respectively (AUC of the ROC curve = 0.828). Conclusions: It was decided that the level of HNP 1-3 in the synovial fluid can be used as an alternative indicator in the diagnosis of septic arthritis.