Elaboration of a new synovial predictive score of septic origin for acute arthritis on the native joint (RESAS).

OBJECTIVE: To establish a new predictive score for the diagnosis of septic arthritis (SA) according to different synovial fluid (SF) variables. METHODS: First, we analysed the different clinical, biological and SF variables associated with the diagnosis of SA (according to the Newman's criteria) in a monocentric cohort of acute arthritis (<30 days) (n = 233) (SYNOLACTATE cohort). A new score predictive of SA (RESAS) was created using the independent discriminant variables after multivariate analysis. A value was attributed to each variable of the score according to the weighting based on their likelihood ratio for the diagnosis of SA. RESAS performance was then tested on the first cohort (internal validation) and then checked on a second independent cohort (n = 70) (external validation). RESULTS: After multivariate analysis, four independent variables of the SF were included for RESAS: (i) purulent SF or white blood cells count ≥70 000/mm3; (ii) absence/presence of crystals; (iii) lactate; and (iv) glucose synovial level. RESAS ranged between -4 and +13 points. The performance of RESAS to predicted SA was excellent with area under the curve (AUC)=0.928 (0.877-0.980) in internal validation and AUC=0.986 (0.962-1.00) in external validation. For a RESAS threshold ≥+4, SA was diagnosed with Se=56.0% (0.371-0.733), Sp=98.1% (0.952-0.993), LR+=29.1 (10.4-81.6) in the first cohort and with Se=91.7% (0.646-0.985), Sp=98.3% (0.909-0.997), LR+=53.2 (7.56-373) in the second cohort. CONCLUSION: RESAS is a new composite score of four SF variables with excellent performance to predicted SA in acute arthritis population.

Performance of a new rapid diagnostic test the lactate/glucose ratio of synovial fluid for the diagnosis of septic arthritis.

OBJECTIVE: To evaluate the diagnostic performance of the synovial lactate, glucose and lactate/glucose ratio assay for the diagnosis of septic arthritis. METHODS: In this monocentric cross-sectional study, synovial fluids were prospectively obtained from patients with acute joint effusion (<30 days) on native joint. Septic arthritis was defined using Newman's criteria. To evaluate diagnostic performance, Receiver Operating Characteristic (ROC) curves with Area under the curve (AUC), Sensitivities (Se), Specificities (Sp), LR+ their 95% confidence intervals were calculated. Synovial fluid cultures with gram staining, crystal analyses, synovial fluid white blood cell counts (WBC), lactate and glucose assays were performed. RESULTS: A total of 233 synovial fluids were included. 25 patients had septic arthritis and 208 had non-septic arthritis (104 crystal-induced arthritis, 15 RA, 8 SpA, 6 reactive arthritis, and 75 acute arthritis of undifferentiated origin). Synovial lactate/glucose ratio performed higher than the synovial lactate or glucose assay separately (AUC: 0.859 [0.772-0.945]). Best synovial lactate/glucose ratio threshold to differentiate septic arthritis from non-septic arthritis was 5 Se 52% [0.34-0.7], Sp 98.1% [0.95-0.99], LR+ 27.0[9.50-76.00]). CONCLUSION: The diagnostic performance of synovial lactate/glucose allows septic arthritis to be effectively and very quickly distinguished from other types of arthritis.