Analysis of synovial inflammatory markers to differ infectious from gouty arthritis.

OBJECTIVES: Septic and gouty arthritis show the same clinical symptoms, but septic arthritis is an orthopedic emergency and needs immediate surgical intervention, whereas a systemic drug therapy is needed in acute gouty arthritis. The aim of this study was to investigate which inflammatory markers allow an accurate differentiation of septic and gouty arthritis.

DESIGN AND METHODS: This was a retrospective examination of serum markers (peripheral white blood cells, C-reactive Protein and uric acid) and inflammatory markers in the synovial fluid (lactate, glucose, uric acid, lactate dehydrogenase, synovial fluid white blood cell count, total protein, and interleukin-6) in 53 patients with culture-verified septic arthritis and 29 with gouty arthritis. Receiver-Operating-Characteristic-curves with corresponding Area under the curve (AUC), sensitivity, specificity, likelihood-ratio and interval likelihood-ratios were calculated to define the diagnostic potential of the inflammatory markers.

RESULTS: Synovial lactate showed the greatest diagnostic potential (AUC = 0.901, sensitivity = 89.5%, specificity = 77.3%, negative likelihood-ratio = 0.14) followed by synovial glucose (AUC=0.853) and synovial uric acid (AUC = 0.841).

CONCLUSIONS: Lactate in the synovial fluid has excellent diagnostic potential to differ septic arthritis from gouty arthritis. Synovial lactate levels above 10 mmol/L almost proofed septic arthritis, lactate levels lower than 4.3 mmol/L make it very unlikely.