A new biochemical score from synovial fluid for diagnosing septic arthritis.

OBJECTIVES

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).

METHODS

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.

RESULTS

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.

CONCLUSION

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.