Which range is most suggestive of septic arthritis based on synovial fluid leukocyte count?

• A. <2000
• B. 2-75,000
• C. 100,000 and above
• D. 50-100,000

Answer: (C)

When a joint infection is possible, the amount of white blood cells in the synovial fluid helps differentiate septic arthritis from other joint troubles. Septic arthritis typically produces a marked neutrophilic response with very high leukocyte counts in the fluid, often exceeding 50,000 cells per microliter and frequently reaching 100,000 or more. Inflammatory or noninfectious joint problems usually fall into much lower ranges, such as around 2,000–50,000, with many noninfectious effusions staying below 50,000. So among the options, the range of 100,000 and above best fits septic arthritis because it reflects the extreme inflammatory response driven by infection.