Diagnosing Septic Arthritis in the Synovial White Cell Count "Gray Zone".

Differentiating septic arthritis of the pediatric hip from other causes of hip pain and effusion continues to present a diagnostic challenge for the clinician. Although septic arthritis traditionally has been reported to have a synovial white blood cell count of 75,000 cells/mm3 or greater, lower counts can be seen in this condition. In cases where a synovial sample has been obtained and the cell count falls in the intermediate range between 25,000 and 75,000 cells/mm(3), it is unclear what proportion of these cases may be truly septic hips. In this evidence-based review, we examine Heyworth et al's study focusing on the predictive value of this intermediate white cell count range in a Lyme-endemic region.