During arthrocentesis, how many white blood cells (WBCs) would typically indicate septic arthritis?

In the context of diagnosing septic arthritis through arthrocentesis, a count of 50,000 white blood cells (WBCs) or more is significant. Elevated WBC counts in the synovial fluid typically suggest an inflammatory or infectious process. Specifically, a count of 50,000 WBCs or higher often indicates a strong possibility of septic arthritis, particularly when a predominance of neutrophils is seen in the fluid analysis.

In septic arthritis, the inflammatory response is robust, which correlates with high WBC counts. Therefore, values at or above this threshold can be used clinically as a marker to prompt further investigations, such as cultures of the synovial fluid to identify causative organisms, or to initiate appropriate antibiotic therapy.

Counts lower than 50,000 may not rule out infection but are less definitive; counts below that range suggest a less likely diagnosis of septic arthritis, especially if the number falls within ranges typical of other conditions such as inflammatory arthritides or crystal arthropathies.