Use of erythrocyte sedimentation rate and C-reactive protein level to diagnose infection before revision total knee arthroplasty. A prospective evaluation.

BACKGROUND: Despite the widespread use of several diagnostic tests, there is still no perfect test for the diagnosis of infection at the site of a total knee arthroplasty. The purpose of this study was to evaluate the diagnostic test characteristics of the erythrocyte sedimentation rate and C-reactive protein level for the assessment of infection in patients presenting for revision total knee arthroplasty.
METHODS: One hundred and fifty-one knees in 145 patients presenting for revision total knee arthroplasty were evaluated prospectively for the presence of infection with measurement of the erythrocyte sedimentation rate and the C-reactive protein level. The characteristics of these tests were assessed with use of two different techniques: first, receiver-operating-characteristic curve analysis was performed to determine the optimal positivity criterion for the diagnostic test, and, second, previously accepted criteria for establishing positivity of the tests were used.
RESULTS: A diagnosis of infection was established for forty-five of the 151 knees that underwent revision total knee arthroplasty. The receiver-operating-characteristic curves indicated that the optimal positivity criterion was 22.5 mm/hr for the erythrocyte sedimentation rate and 13.5 mg/L for the C-reactive protein level. Both the erythrocyte sedimentation rate (sensitivity, 0.93; specificity, 0.83; positive likelihood ratio, 5.81; accuracy, 0.86) and the C-reactive protein level (sensitivity, 0.91; specificity, 0.86; positive likelihood ratio, 6.89; accuracy, 0.88) have excellent diagnostic test performance.
CONCLUSIONS: The erythrocyte sedimentation rate and the C-reactive protein level provide excellent diagnostic test information for establishing the presence or absence of infection prior to surgical intervention in patients with pain at the site of a knee arthroplasty.