A 62-year-old woman with rheumatoid arthritis presents with an acutely swollen painful right knee. Synovial fluid analysis shows WBC 65,000 cells per microlitre with 90 percent neutrophils. Gram stain shows no organisms. Which statement best guides management?

• A The count is too low for septic arthritis and gout is the likely diagnosis
• B Counts above 50,000 cells per microlitre strongly suggest septic arthritis even if Gram stain is negative ✓
• C Rheumatoid flare reliably produces counts above 60,000 cells per microlitre
• D Aspiration should be repeated after one week before starting any treatment

Explanation

Synovial WBC above 50,000 cells per microlitre with neutrophil predominance strongly favours septic arthritis, and counts above 100,000 are near diagnostic. Gram stain is negative in a substantial proportion of culture-proven cases, so a negative stain never excludes infection. Rheumatoid flares usually produce lower counts, typically under 20,000, which kills option C. Empirical antibiotics and drainage should not be delayed for repeat aspiration.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.