Abstract
Background: Synovial pH, lactate, and glucose are established biomarkers for septic arthritis in native joints and have emerging utility in periprosthetic joint infection (PJI). In routine care, these biomarkers are commonly analyzed in central laboratories, which may delay clinical decision-making. Blood gas analyzers (BGAs), which can also measure these parameters, are widely available at the point of care, and their use could accelerate decision-making. However, BGAs are not validated for synovial fluid analysis. Materials and methods: This prospective analytical agreement study included 35 consecutive patients undergoing knee joint aspiration for suspected PJI or septic arthritis of the native joint. Each sample was measured in triplicate both in the central laboratory and using a BGA. The agreement between the two methods was assessed using Passing-Bablok and Bland-Altman analyses. The study was designed to assess analytical agreement between both methods rather than diagnostic accuracy. Results: BGA measurements for synovial pH, lactate, and glucose demonstrated good to excellent agreement with those obtained using central laboratory methods. Agreement was excellent for synovial glucose and overall good for lactate, with negligible mean bias. Linear regression showed very strong correlations for glucose ( r = 0.997) and lactate ( r = 0.989). Synovial pH showed greater variability, with a mean bias of - 0.10 pH units; however, repeatability analysis revealed lower within-sample variability for BGA-based pH measurements compared with laboratory pH measurements. Conclusion: BGAs enable rapid, reliable measurement of synovial pH, lactate, and glucose from small sample volumes and may support timely clinical decision-making in suspected septic arthritis and PJI. Further studies should assess inter-device generalizability and establish device-specific reference ranges.