Background: The erythrocyte sedimentation rate, the C-reactive
protein serum level, and the white blood-cell count are routinely used to
diagnose periprosthetic infection. In the present study, the diagnostic
accuracy of the interleukin-6 serum level was compared with the accuracy of
these standard tests for the evaluation of a group of patients who had had a
total hip or total knee arthroplasty and were undergoing a reoperation for the
treatment of an infection or another implant-related problem.
Methods: A prospective, case-control study of fifty-eight patients
who had had a total hip or knee replacement and were undergoing a reoperation
because of an infection (seventeen patients) or another implant-related
problem (forty-one patients) was conducted. The serum levels of interleukin-6
and C-reactive protein, the erythrocyte sedimentation rate, and the white
blood-cell count were measured. The definitive diagnosis of an infection was
determined on the basis of positive histopathological evidence of infection
and growth of bacteria on culture of intraoperative specimens. Two-sample
Wilcoxon rank-sum (Mann-Whitney) tests were used to determine the presence of
a significant difference between patients with and without infection with
regard to each laboratory value studied. The sensitivity, specificity,
positive predictive value, negative predictive value, and accuracy of each
text were also calculated.
Results: The serum interleukin-6 level, erythrocyte sedimentation
rate, and C-reactive protein level were significantly higher in patients who
had an infection than in those who did not, both when all patients were
considered together and when the total hip arthroplasty and total knee
arthroplasty groups were considered separately. With the numbers available,
there was no significant difference with regard to the white blood-cell count
between patients with and without infection. With a normal serum interleukin-6
level defined as <10 pg/mL, the serum interleukin-6 test had a sensitivity,
specificity, positive predictive value, negative predictive value, and
accuracy of 1.0, 0.95, 0.89, 1.0, and 97%, respectively.
Conclusions: An elevated serum interleukin-6 level correlated
positively with the presence of periprosthetic infection in patients
undergoing a reoperation at the site of a total hip or knee arthroplasty. The
serum interleukin-6 level is valuable for the diagnosis of periprosthetic
infection in patients who have had a total hip or total knee arthroplasty.
Level of Evidence: Diagnostic Level IV. See Instructions
to Authors for a complete description of levels of evidence.