The relationship of C-reactive protein/interleukin-6 concentrations between serum and synovial fluid in the diagnosis of periprosthetic joint infection

Ji-Ying Chen,Yong-Gang Zhou,Rui Li,Wei Chai,Bao-Zhan Yu,Xiang Li

doi:10.1186/s13018-021-02880-x

Abstract

BackgroundThe relationship of C-reactive protein (CRP)/interleukin-6 (IL-6) concentrations between serum and synovial fluid and whether synovial CRP/IL-6 testing in addition to serum CRP/IL-6 testing would result in a benefit in the diagnosis of periprosthetic joint infection (PJI) deserves to be investigated.MethodsFrom June 2016 to July 2019, 139 patients were included in the study. Synovial CRP and IL-6 were tested by ELISA. The serum CRP and IL-6 were obtained from medical records. The definition of PJI was based on the modified Musculoskeletal Infection Society (MSIS) criteria. The relationship of serum and synovial CRP and IL-6 and the value of each index in the diagnosis of PJI were evaluated.ResultsThe receiver operating characteristic (ROC) curves showed that synovial IL-6 had the highest area under the curve (AUC) at 0.935, which was followed by synovial CRP, serum IL-6 and serum CRP 0.861, 0.847 and 0.821, respectively. When combining serum CRP and synovial CRP to diagnose PJI, the AUC was 0.849, which was slightly higher than the result obtained when using serum CRP alone. In contrast, when combining serum IL-6 and synovial IL-6 to diagnose PJI, the AUC increased to 0.940, which was significantly higher than that obtained using serum IL-6 alone.ConclusionThe synovial IL-6 has the highest diagnostic accuracy for PJI. However, inferring the level of CRP/IL-6 in the synovial fluid from the serum level of CRP/IL-6 was not feasible. Synovial CRP testing did not offer an advantage when combined with an existing serum CRP result to diagnose PJI, while additional synovial IL-6 was worthy of testing even if there was an existing serum IL-6 result.

Highlights

Periprosthetic joint infection (PJI) is a serious complication after total knee or hip arthroplasties and is associated with a large economic burden on healthcare systems and increased morbidity and mortality [1, 2]
Among the 139 included patients, 62 patients were diagnosed with periprosthetic joint infection (PJI), and 77 patients were not diagnosed with PJI based on the modified Musculoskeletal Infection Society (MSIS) criteria
The receiver operating characteristic (ROC) curves showed that synovial IL-6 had the highest area under the curve (AUC), at 0.935, which was followed by the AUCs of synovial C-reactive protein (CRP), serum IL-6 and serum CRP: 0.861, 0.847 and 0.821, respectively (Fig. 2)

Summary

Introduction

Periprosthetic joint infection (PJI) is a serious complication after total knee or hip arthroplasties and is associated with a large economic burden on healthcare systems and increased morbidity and mortality [1, 2]. It. Among the various kinds of tests, using serum markers would be simpler and more practical than other methods. Serum markers are often used as a first-line screening method. Numerous serum markers, such as erythrocyte sedimentation rate (ESR), C-reactive protein. Synovial fluid tests such as white blood cell [WBC] count and differential, interleukin-6 (IL-6), a-defensin are often needed to further clarify the diagnosis. The relationship of C-reactive protein (CRP)/interleukin-6 (IL-6) concentrations between serum and synovial fluid and whether synovial CRP/IL-6 testing in addition to serum CRP/IL-6 testing would result in a benefit in the diagnosis of periprosthetic joint infection (PJI) deserves to be investigated

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