Interleukin-6 in two-stage revision arthroplasty: what is the threshold value to exclude persistent infection before re-implanatation?

The purpose of this study was to evaluate whether the serum level of interleukin 6 (IL-6) could be used to identify the persistence of infection after the first stage of a two-stage revision for periprosthetic joint infection. Between 2010 and 2011, we prospectively studied 55 patients (23 men, 32 women; mean age 69.5 years; 36 to 86) with a periprosthetic joint infection. Bacteria were identified in two intra-operative tissue samples during re-implantation in 16 patients. These cases were classified as representing persistent infection. To calculate a precise cut-off value which could be used in everyday clinical practice, a 3 x 2 contingency table was constructed and manually defined. We found that a serum IL-6 ≥ 13 pg/mL can be regarded as indicating infection: its positive-predictive value is 90.9%. A serum IL-6 ≤ 8 pg/mL can be regarded as indicating an absence of infection: its negative predictive value is 92.1%. The serum IL-6 level seems to be a reasonable marker for identifying persistent infection after the first stage of a revision joint arthroplasty and before attempting re-implantation. ©2015 The British Editorial Society of Bone & Joint Surgery.