Can Serum Procalcitonin Help to Differentiate Between Septic and Nonseptic Arthritis?

Purpose: The aim of this study was to evaluate the usefulness of serum procalcitonin (PCT) to differentiate between septic and nonseptic acute arthritis. Methods: Thirty-three patients who presented to our outpatient clinics with the symptoms of acute arthritis of unknown origin were enrolled in this study. We determined the serum concentrations of PCT and C-reactive protein and performed a white blood cell count. The definitive diagnosis was determined by microbiologic examination of a joint aspirate. Results: Microbiologic cultures showed that 15 patients had septic arthritis. In these patients the PCT levels were significantly increased compared with those in the 18 patients with nonseptic arthritis (mean ± SD, 1.18 ± 1.66 ng/mL v 0.078 ± 0.073 ng/mL; P = .001). On the basis of the normal range (<0.5 ng/mL), the test sensitivity in our series was 53.3% with a specificity of 100%. C-reactive protein levels in patients with septic arthritis were also significantly elevated compared with the nonseptic group. Because in either group no value was within the normal range (<0.5 mg/dL), the specificity was 0%. Conclusions: In this study serum PCT levels of patients with septic arthritis were significantly higher than those of patients with nonseptic arthritis (P = .001). However, the sensitivity when referencing the normal upper limit of PCT (0.5 ng/mL) is not high enough to establish a diagnosis based exclusively on serum parameters. This reflects the results of other studies examining localized infections without generalized bacteremia. The data suggest that a specific PCT cutoff level for localized infections could be helpful in the future. Level of Evidence: Level III, diagnostic study of nonconsecutive patients without consistently applied reference gold standard.