Synovial pH, lactate, and glucose as adjunct biomarkers to exclude periprosthetic joint infection in hip and knee arthroplasty: a prospective study

<b>Background</b>: Synovial pH, glucose, and lactate have been studied in native joint septic arthritis, but studies in periprosthetic joint infection (PJI) are limited. The purpose of this study is to evaluate the diagnostic utility of synovial pH, lactate, and glucose as potential diagnostic biomarkers for PJI. <b>Materials and methods</b>: Joint aspirations were performed in 100 consecutive patients (24 hips, 76 knees) with suspected PJI. In our cohort, 36 % were diagnosed with PJI, while 64 % were classified as uninfected based on the EBJIS criteria of 2021. Receiver operating characteristic (ROC) curves and Youden's index were employed to determine the optimal thresholds for synovial pH, lactate, and glucose. <b>Results</b>: The mean synovial pH was significantly lower in the PJI group compared to the uninfected group (7.23 vs. 7.49; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>p</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0.009</mml:mn></mml:mrow> </mml:math> ). The mean synovial lactate was significantly higher in the PJI group compared to the uninfected group (8.81 vs. 6.28; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>p</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0.008</mml:mn></mml:mrow> </mml:math> ). The mean synovial glucose was significantly lower in the PJI group compared to the uninfected group (41.4 vs. 62.1; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>p</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0.027</mml:mn></mml:mrow> </mml:math> ). The optimal thresholds for synovial pH, lactate, and glucose were 7.25, 8.45 mmol L^-1 and 18 mg dL^-1 with a sensitivity of 50 %, 50 %, and 30 % as well as a specificity of 81 %, 84 %, and 96 %, respectively. The combined use of all three biomarkers yielded a negative predictive value of 84 % for the diagnosis of PJI. <b>Conclusion</b>: Synovial pH, lactate, and glucose may serve as valuable adjunct parameters in the diagnosis of PJI with a high negative predictive value.