Clinical Health Updates

Synovial WBC and percent PMNs best for septic arthritis diagnosis

Clinical Question:
What are the most useful symptoms, signs, and laboratory tests for diagnosing septic arthritis in adults presenting with an acutely painful and swollen joint?

Bottom Line:
Clinical findings identify patients with peripheral, monoarticular arthritis who might have septic arthritis. However, the synovial WBC and percentage of polymorphonuclear cells from arthrocentesis are required to assess the likelihood of septic arthritis before the Gram stain and culture test results are known.

Reference:
Margaretten ME, Kohlwes J, Moore D, Bent S. Does this patient have septic arthritis? JAMA 2007;297:1478-1488.

Study Design:
Systematic review

Synopsis:
In patients who present with an acutely painful and swollen joint, prompt identification and treatment of septic arthritis can substantially reduce morbidity and mortality. The investigators reviewed the accuracy and precision of the clinical evaluation for the diagnosis of nongonococcal bacterial arthritis. Data has been gathered from PubMed and EMBASE searches (1966 through January 2007), limited to human, English-language articles and using the following Medical Subject Headings terms: arthritis, infectious, physical examination, medical history taking, diagnostic tests, and sensitivity and specificity. Studies were included if they contained original data on the accuracy or precision of historical items, physical examination, serum, or synovial fluid laboratory data for diagnosing septic arthritis. Three authors independently abstracted data from the included studies. Fourteen studies involving 6242 patients, of whom 653 met the gold standard for the diagnosis of septic arthritis, satisfied all inclusion criteria. Two studies examined risk factors and found that age, diabetes mellitus, rheumatoid arthritis, joint surgery, hip or knee prosthesis, skin infection, and human immunodeficiency virus type 1 infection significantly increase the probability of septic arthritis. Joint pain (sensitivity, 85%; 95% confidence interval [CI], 78%-90%), a history of joint swelling (sensitivity, 78%; 95% CI, 71%-85%), and fever (sensitivity, 57%; 95% CI, 52%-62%) are the only findings that occur in more than 50% of patients. Sweats (sensitivity, 27%; 95% CI, 20%-34%) and rigors (sensitivity, 19%; 95% CI, 15%-24%) are less common findings in septic arthritis. Of all laboratory findings readily available to the clinician, the 2 most powerful were the synovial fluid white blood cell (WBC) count and percentage of polymorphonuclear cells from arthrocentesis. The summary likelihood ratio (LR) increased as the synovial fluid WBC count increased (for counts <25,000/microl:> or =25,000/microL: LR, 2.9; 95% CI, 2.5-3.4; for counts >50,000/microL: LR, 7.7; 95% CI, 5.7-11.0; and for counts >100,000/microL: LR, 28.0; 95% CI, 12.0-66.0). On the same synovial fluid sample, a polymorphonuclear cell count of at least 90% suggests septic arthritis with an LR of 3.4 (95% CI, 2.8-4.2), while a polymorphonuclear cell count of less than 90% lowers the likelihood (LR, 0.34; 95% CI, 0.25-0.47).