Though CRP and ESR levels are significantly higher in patients that have septic arthritis, a 1998 study showed that there is extensive overlap between patients with septic arthritis crystal assoicated arthritis that both CRP and ESR have low sensitivity, specificity and predictive values. Peripherial WBC counts did not differ between the two disease processes..
The morale of the story: If you are suspecting septic arthritis you need to perform an arthorcentesis to analysis the synovial fluid. Systemic biomarkers can not support one diagnosis over the other.
References
Soderquist B, Jones I, Fredlund H, Vikerfors T: Bacterial or crystal-associated arthritis? Discriminating ability of serum inflammatory markers. Scand J Infect Dis 1998; 30: 591-596.
