Fourteen studies (n=6,242) were included in the review. The sample size ranged from 41 to 4,889.
Only 3 studies were classified as quality score 1, level 1; most studies used an adequate reference standard.
Risk factors (2 studies).
The following risk factors were found to be associated with septic arthritis: age, diabetes mellitus, rheumatoid arthritis, joint surgery, hip or knee prosthesis, and skin infection in combination with joint prosthesis. Infection with the human immunodeficiency virus (HIV) increased the probability of septic arthritis.
Signs and symptoms (7 studies).
The only symptoms with sensitivity greater than 50% were joint pain (sensitivity 0.85, 95% CI: 0.78, 0.90; 2 studies), a history of joint swelling (sensitivity 0.78, 95% CI: 0.71, 0.85; 2 studies) and fever (sensitivity 0.57, 95% CI: 0.52, 0.62; 7 studies). None of these studies assessed specificity.
Serum laboratory values (2 studies).
Abnormal peripheral WBC count, erythrocyte sedimentation rate and C-reactive protein had limited accuracy (the positive LRs ranged from 1.3 to 1.6).
Synovial WBC counts (5 studies).
WBC counts above 100,000/microL showed good accuracy for ruling in septic arthritis but poor accuracy for ruling out the condition: the sensitivity ranged from 13 to 40% and specificity from 93 to 100%. As the threshold to define a positive WBC count decreased, sensitivity increased but at the expense of specificity.
Polymorphonuclear cells (4 studies).
The presence of 90% or more polymorphonuclear cells showed poor accuracy, both for ruling in and ruling out septic arthritis: the sensitivity ranged from 57 to 92% and specificity from 68 to 83%.
Other synovial fluid laboratory test results (3 studies).
Low glucose had poor sensitivity (38 to 64%) and moderate specificity (85%). The presence of protein in synovial fluid showed very poor sensitivity and specificity (pooled sensitivity 48%, pooled specificity 46%; 2 studies). The presence of lactate dehydrogenase in synovial fluid showed excellent sensitivity (100%) but poor specificity (51%).