Comparative Analysis of Laboratory Markers of Synovial Fluid in the Verification of Periprosthetic Joint Infection

Introduction & Aim With the increasing number of revision large joint arthroplasties, a reliable differential diagnosis between aseptic instability and periprosthetic joint infection is critical, as the treatment strategies for these conditions differ fundamentally. Verification of infectious joint lesions requires a comprehensive approach that goes beyond the assessment of systemic inflammatory markers. Analysis of the synovial fluid status is of primary diagnostic importance: cell counts over 2,000-3,000 cells/μL with pronounced neutrophilia, a positive leukocyte esterase test (LE), and direct pathogen identification by microbiological culture. The aim of the study was to establish a correlation between changes in the cellular composition of synovial fluid and the nature of the identified microflora in patients with suspected joint infections. Methods In 2025, cytological examination results from 84 synovial fluid samples (78 patients) were analyzed. Based on a combination of clinical data and systemic inflammatory markers, suspected infection was confirmed in 42% of patients (n=33), who underwent bacteriological examination in addition to cytology. Synovial fluid aspirates obtained from patients with suspected joint infection at the prehospital and in-hospital stages of care served as the study material. Results Leukocyte esterase levels were analyzed in 47 cases. LE values varied widely, from 15 to 500 units. Values above 25 were always associated with a positive bacteriological culture. A specific relationship between marker levels and the type of pathogen was noted. Gram-negative microflora were characterized by borderline LE values (15-25 units), while infection with gram-positive microorganisms was accompanied by a significant increase in this value (from 25 to 500 units). It was found that 50% of the identified gram-positive microflora strains were resistant to beta-lactam antibiotics. An increase in the cytosis level above reference values was recorded in 60.7%. Quantitative indicators ranged from 200 to 500,000 cells/μL. It was found that the increase in cellularity was accompanied by significant neutrophilia, ranging from 76% to 95%. Conclusions Cytological analysis (cytosis >2900 cells/μL and neutrophilia 76–95%) is a highly sensitive predictor of infection, allowing for the verification of the inflammatory process even before bacterial culture results are available. A LE level above 25 units demonstrated an absolute correlation with the presence of microflora. High values (up to 500 units) are characteristic of gram-positive flora, while gram-negative microorganisms are associated with borderline values (15–25 units). The identified high proportion of strains resistant to beta-lactam antibiotics (50% of gram-positive pathogens) necessitates mandatory antibiogram testing to optimize etiotropic therapy.