How sensitive is the synovial fluid white blood cell count in diagnosing septic arthritis?

McGillicuddy, Daniel C.; Shah, Kaushal H.; Friedberg, Ryan P.; Nathanson, Larry A.; Edlow, Jonathan A.

doi:10.1016/j.ajem.2006.12.001

« Previous Next »American Journal of Emergency Medicine
Volume 25, Issue 7 , Pages 749-752, September 2007

How sensitive is the synovial fluid white blood cell count in diagnosing septic arthritis?

Daniel C. McGillicuddy, MD
- Department of Emergency Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA
- Corresponding author.
Kaushal H. Shah, MD
- Department of Emergency Medicine, St. Luke's Roosevelt Hospital, University Hospital of Columbia University, College of Physicians and Surgeons, New York, NY, USA
Ryan P. Friedberg, MD
- Department of Emergency Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA
Larry A. Nathanson, MD
- Department of Emergency Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA
Jonathan A. Edlow, MD
- Department of Emergency Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA

Received 22 May 2006; received in revised form 7 December 2006; accepted 7 December 2006.

Abstract

Objective

This study was conducted to determine the sensitivity of the current standard for synovial fluid leukocytosis analysis in diagnosing infectious arthritis or a septic joint. How accurate is the standard synovial fluid white blood cell (WBC) cutoff of 50000 WBC/mm³ to rule out septic arthritis?

Methods

We conducted a retrospective study at an urban tertiary care medical center with 50000 adult emergency department visits per year. The study population consisted of patients with infectious arthritis confirmed by synovial fluid culture growth of a pathogenic organism. The study period lasted from January 1996 to December 2002. Extracted data included synovial fluid leukocyte count, Gram's stain, culture, past medical history, and discharge diagnosis. Fisher exact test was used to compare proportions. Sensitivity and means were calculated with 95% confidence intervals (CI).

Results

There were 49 culture-positive synovial fluid aspirates in the 6-year study period. Nineteen (39%) of 49 patients (95% CI, 25%-52%) had a synovial WBC of less than 50000/mm³ and 30 (61%) of 49 patients (95% CI, 48%-75%) had a synovial WBC of more than 50000/mm³. The sensitivity of the 50000 synovial WBC/mm³ cutoff was 61% (95% CI, 48%-75%). Twenty-seven (55%) of 49 patients had a negative Gram's stain (95% CI, 41%-69%) and 15 (56%) of 27 patients (95% CI, 37%-74%) with negative Gram's stain had a synovial WBC of less than 50000/mm³.