The QuickLine IL-6 lateral flow immunoassay improves the rapid intraoperative diagnosis of suspected periprosthetic joint infections.

BACKGROUND: When deciding upon the best treatment strategy in revision arthroplasty, it is absolutely crucial to use the best possible preoperative detection whether a periprosthetic joint infection (PJI) is present or not. New molecular markers investigated in serum samples and synovial fluid can help to improve the preoperative diagnosis. In 2001, a novel IL-6 lateral flow immunoassay testing device was introduced which has never been tested in synovial fluid so far.
OBJECTIVE: For our study we investigated whether the test can be used safely, feasibly and time effectively with synovial fluid gathered from potentially infected THAs or TKAs and whether the already published cutoff for IL-6 in synovial fluid predicting a PJI can be reproduced using the QuickLine IL-6 immunoassay.
METHODS: After ethic approval and within the scope of a prospective controlled trial we investigated 26 patients (m = 9, 34.6%; f= 17, 65.4%) with n = 13 (50%) potentially infected total hip arthroplasties (THAs) and n = 13 (50%) suspected PJIs of total knee arthroplasties (TKAs). Sterile aspirated synovial fluid was examined for total leukocyte count and cell differentiation by a blood count analyzer in body fluid mode as well as for IL-6 (Immulite, Siemens Medical Solutions Diagnostics GmbH, Eschborn, Germany). Another part of the joint aspirate was tested using the QuickLine IL-6 Test by Milenia Biotec (Milenia Biotec, Gießen, Germany).
RESULTS: The mean concentration of IL-6 as determined from our reference laboratory testing (Siemens Immulight) for aseptic cases was 1,219 pg/mL (SD 1,369 pg/mL, min 134 pg/mL-max 4,214 pg/mL). The mean IL-6 concentration measured via the IL-6 QuickLine for aseptic cases was 410 pg/mL (SD 371 pg/mL, min 100 pg/mL-max 1562 pg/mL). The test showed no false negative or false positive results in the cases tested. In six patients, PJI was considered proven. The QuickLine Test indicated IL 6 concentrations > 10,000 pg/mL in these cases without further quantification above this maximum detection threshold. Results from the QuickLine Test and the laboratory tests were matched and a non-linear best fit curve (log-log-curve) was applied. The subsequent Spearman correlation showed a correlation coefficient of r = 0.92 (95% CI 0.81-0.97) which corresponds to a two-tailed p-value of < 0.0001, respectively. As a primary finding we were able to show that the Milenia QuickLine IL-6 Test can be used safely, feasibly and time effectively with synovial fluid gathered intraoperatively from potentially infected THAs or TKAs. The test as provided worked well in 84.6% of the samples tested and failed only due to very viscous synovial fluid. As a secondary result we found that the previously published cut-off for IL-6 in synovial fluid predicting a PJI with a sensitivity of 46.88% and a specificity of 97.62% can be reproduced using the QuickLine IL-6 immunoassay.
CONCLUSION: Taking the limitations of the low sample size as a given this relatively simple point of care (POC) assay showed promising results in our pilot trial and may help diagnosing PJI. It may help physicians and surgeons to choose the best and least invasive treatment strategy for patients presenting with painful arthroplasty.