Objectives: We investigated the correlation between the laboratory results of the synovial fluid and the clinical features of the affected joints to find which clinical findings are suggestive of septic arthritis.

Patients and methods: Retrospective study of 267 joint fluid tests which have been done during the period 2000–2001 from knee hydrathrosis of 256 patients (86 men and 170 women, 19–81 years of age). We found clinical evidence for 183 hydrathrosis (176 patients) due to rheumatoid arthritis 63, psoriatic arthritis 24, reactive arthritis 36, uric acid arthritis 9, ankylosing spondylitis 6 and osteoarthritis 45. We correlated the clinical and the macroscopic and microscopic findings of joint fluid.

The statistical analysis was done by x-square test.

Results: Septic arthritis supposed to 86 hydrathrosis (46,9%) but the analysis of synovial fluid showed only at 8 (4,37%) p< 0.001.

Conclucions: The fever, the macroscopic image of puriform joint fluid, and the combination of warmth with redness are strong evidence for septic arthritis. So if the above findings are present we must wait for Gram stain and culture before the cortisone intraarticular infusion.