Measuring synovial fluid procalcitonin levels in distinguishing cases of septic arthritis, including prosthetic joints, from other causes of arthritis and aseptic loosening

Objectives Differentiating septic arthritis from non-septic arthritis can be challenging as the clinical pictures are similar and an efficacious diagnostic test is not yet available. Our objectives in this study were to establish if procalcitonin (PCT) could be reproducibly measured from synovial fluid, if there is a difference in synovial procalcitonin values between patients with septic and non-septic arthritis, respectively, including those with implants and to determine cut-off levels that could be used as a practical tool in the management of these conditions. Methods Using a standard serum assay, synovial fluid PCT levels were measured retrospectively in 26 septic and 50 non-septic predefined arthritis cases. The reproducibility of synovial PCT was also assessed at various concentrations. Results Synovial PCT can be measured and is reproducible. In this cohort, statistically significant higher synovial PCT levels were found in cases of septic arthritis than in non-septic arthritis. Sensitivities, specificities and positive and negative predictive values varied at different cut-off levels. Conclusion The test could be added to other microbiological and biochemical tests and may be used to supplement other clinical, radiological and laboratory findings in the assessment of patients with acute painful joints. In our cohort, findings of very high synovial PCT levels supported an infection process, including in prosthesis-related infections. The high negative predictive value of low synovial PCT levels could exclude infection in both native and prosthetic joints. Larger prospective studies are needed to further validate these results and to examine the cost effectiveness of synovial PCT.