Combining C-reactive Protein and Interleukin-6 May Be Useful to Detect Periprosthetic Hip Infection

BACKGROUND: The sensitivity and specificity to detect periprosthetic infection of the different methods have been questioned, and no single laboratory test accurately detects infection before revision arthroplasty. QUESTIONS/PURPOSES: We asked whether preoperative C-reactive protein (CRP) and interleukin-6 (IL-6) could lead to similar sensitivity, specificity, and predictive values as our previous results obtained with intraoperative frozen section (FS) in revision total hip arthroplasty (THA). METHODS: We prospectively followed 69 patients who had undergone revision THA for failure of a primary THA. The definitive diagnosis of an infection was determined on the basis of positive histopathologic evidence of infection or growth of bacteria on culture. RESULTS: Eleven of the 69 hips were infected. The combination of an elevated CRP and IL-6 was correlated with deep infection in all the cases and showed a sensitivity of 0.57 (0.13-1.00), a specificity of 1.00 (0.99-1.00), a positive predictive value of 1.00 (0.87-1.00), and a negative predictive value of 0.94 (0.87-1.00). FS showed a sensitivity of 0.81 (0.54-1.00), a specificity of 0.98 (0.94-1.00), a positive predictive value of 0.90 (0.66-1.00), and a negative predictive value of 0.96 (0.91-1.00). Combining CRP and IL-6 provided similar sensitivity, specificity, and positive predictive values as the FSs. CONCLUSIONS: Our data suggest the combination of CRP and IL-6 would be a useful serologic tool to complement others when diagnosing periprosthetic infection.