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Combined use of ESR, CRP effective screening tool for ruling out periprosthetic infection after TKA, researchers find

Monday, January 28 2008 | Comments

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What's This? The combined use of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) as a screening tool is an effective strategy for ruling out a diagnosis of periprosthetic infection following total knee arthroplasty (TKA), according to the results of a new study.

The researchers noted that periprosthetic infection can be an occult cause of pain, and that its diagnosis is challenging because no one test has consistently demonstrated high sensitivity and specificity. To address this issue, they examined whether ESR and CRP in combination were reliable screening tests for infection in patients with a painful TKA.

The study included 296 patients (mean age, 66 years) who had undergone total knee revision. All of the subjects had a preoperative ESR and CRP performed, in addition to preoperative or intraoperative cultures. A knee was considered infected if the culture was positive or if both the leukocyte count was >1,760 cells/mcL and polymorphonuclear cells were >73%, or there was a draining sinus tract or abscess present.

None of the patients had a separate condition associated with elevated inflammatory markers.

Among the participants, 116 (39%) were classified as having an infected knee. For these patients, the mean ESR was 85 mm/hour (elevated ESR defined as >30 mm/hr) and the mean CRP was 110 mg/L (elevated CRP defined as >10 mg/L). On the other hand, the patients who were not infected had respective ESR and CRP values of 22 mm/hr and 7 mg/L.
Of note, 5 patients who were classified as having infected knees had normal ESR and CRP values; cultures confirmed infection in 4 of these 5 cases.

Overall, combined ESR and CRP testing had high sensitivity (0.96) and high negative predictive value (0.95).
"[W] e suggest that every patient presenting with a painful TKA be evaluated for periprosthetic infection," the study authors concluded. "ESR and CRP, when used in combination, is a test with high sensitivity, negative predictive value, and low cost ($79 for both tests), which makes this an ideal screening test. Unlike aspiration, it does not subject the patient to the potential introduction of bacteria into a noninfected joint." (Austin MS, et al. J Arthroplasty 2008;23:65-68.)

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