A new biochemical score from synovial fluid for diagnosing septic arthritis

To evaluate the diagnostic performance of synovial fluid (SF) biochemical markers and assess the value of combining their measurements into a composite score for identifying septic arthritis (SA).

Patients who underwent arthrocentesis with SF biochemical analysis (proteins, glucose, lactate dehydrogenase (LDH), lactate) were included in the initial cohort (IC) (May 2018-May 2021) or the validation cohort (June 2021-March 2023). Using IC data, we compared marker levels in SA vs. non-SA and vs. crystal-related arthritis (C-rA) subgroup. Based on receiver operating characteristic (ROC) curves, we identified two thresholds (one optimizing sensitivity, the other specificity) to assign a score of 0-2 for each biomarker. We developed a composite score by combining the individual scores for discriminative biomarkers and assessed its diagnostic performance.

We included 190 SF (170 patients) in the IC; 36 SF (18.9%) were septic. Glucose level was lower in SA than non-SA and C-rA, but lactate and LDH levels were higher (P<0.001). The composite score was developed with a 0-6 scale, with the following thresholds: glucose (≤7 and ≤1.5mmol/L), lactate (≥4.5 and ≥7.5mmol/L), and LDH (≥600 and ≥1200 UI/L). A composite score ≥3 had 100% sensitivity and 73.9% specificity for SA diagnosis in the IC cohort, and a score≥5 had 55.5% sensitivity and 97.8% specificity. These findings were consistent in the validation cohort.

A combined score based on SF markers including glucose, LDH, and lactate may be an effective method for rapidly ruling out SA. A multicentric study is warranted to confirm these results.