Effect of Antibiotic Administration Before Joint Aspiration on Synovial Fluid White Blood Cell Count in Native Joint Septic Arthritis.

Background: This study was performed to assess the impact of preaspiration antibiotics on synovial fluid analysis and timing of operative treatment in native-joint septic arthritis.

Methods: We performed a retrospective record review of adult patients from an urban level 1 trauma center with native joint septic arthritis in 2015-2019, identified by means of codes from the ( and ). Univariate and multivariate analyses were performed to determine whether antibiotics were associated with lower synovial fluid white blood cell counts (WBCs), the percentage of polymorphonuclear neutrophil (PMNs), and rate of culture positivity. Secondary analysis included time elapsed from aspiration to surgery.

Results: Of the 126 patients with septic joints included, nearly two-thirds (n = 80 [63.5%]) received antibiotics before joint aspiration. The synovial fluid WBC count, percentage of PMNs, and rate of culture positivity were significantly lower in patients who received preaspiration antibiotics than in those who did not (mean WBC count, 51 379.1/μL [standard deviation, 52 576.3/μL] vs 92 162.7/μL [59 330.6/μL], respectively [ < .001]; PMN percentage, 83.6% [20.5%] vs 91.9% [6.0%; = .01]; and culture positivity, 32.5% vs 59.1% [ = .008]). Multivariable analyses revealed that these associations remained after controlling for potential confounders (change in PMNs, -42 784.60/μL [95% confidence interval, -65 355/μL to -20 213.90/μL [ < .001]; change in PMNs, -7.8% [-13.7% to -1.8%] [ = .01]; odds ratio, 0.39 [.18-.87; = .02). Patients with a synovial fluid WBC count ≤50 000/μL experienced significant delay in time from joint aspiration to operative intervention (mean [standard deviation], 10.5 [11.3] vs 17.9 [17.2] hours; = .02).

Conclusions: The administration of antibiotics before joint aspiration for suspected septic arthritis appears to decrease the synovial fluid WBC count, the percentage of PMNs, and the rate of culture positivity. Efforts to limit antibiotic administration before joint aspiration are important to minimize diagnostic dilemmas and circumvent treatment delays.