Synovial fluid interleukin-6 is not superior to cell count and differential in the detection of periprosthetic joint infection

Abstract

Aims Synovial fluid white blood cell (WBC) count and percentage of polymorphonuclear cells (%PMN) are elevated at periprosthetic joint infection (PJI). Leucocytes produce different interleukins (IL), including IL-6, so we hypothesized that synovial fluid IL-6 could be a more accurate predictor of PJI than synovial fluid WBC count and %PMN. The main aim of our study was to compare the predictive performance of all three diagnostic tests in the detection of PJI. Methods Patients undergoing total hip or knee revision surgery were included. In the perioperative assessment phase, synovial fluid WBC count, %PMN, and IL-6 concentration were measured. Patients were labeled as positive or negative according to the predefined cut-off values for IL-6 and WBC count with %PMN. Intraoperative samples for microbiological and histopathological analysis were obtained. PJI was defined as the presence of sinus tract, inflammation in histopathological samples, and growth of the same microorganism in a minimum of two or more samples out of at least four taken. Results In total, 49 joints in 48 patients (mean age 68 years (SD 10; 26 females (54%), 25 knees (51%)) were included. Of these 11 joints (22%) were infected. The synovial fluid WBC count and %PMN predicted PJI with sensitivity, specificity, accuracy, PPV, and NPV of 82%, 97%, 94%, 90%, and 95%, respectively. Synovial fluid IL-6 predicted PJI with sensitivity, specificity, accuracy, PPV, and NPV of 73%, 95%, 90%, 80%, and 92%, respectively. A comparison of predictive performance indicated a strong agreement between tests. Conclusions Synovial fluid IL-6 is not superior to synovial fluid WBC count and %PMN in detecting PJI. Level of Evidence: Therapeutic Level II Cite this article: Bone Jt Open 2020;1-12:737–742.

Synovial pH Is As Specific As Synovial Leukocyte Count But Less Sensitive For The Diagnosis of Chronic Prosthetic Joint Infection

“…For our cohort the speci city of WBC count (88%) and PMN% (98%) was as high as for pH (89%), whereas the sensitivity was best for WBC count (90%), but lower for PMN% (73%) and pH (53%). However, other institutions [12] or authors [23] recommend lower cut-off values to detect low-grade infections due to the fact, that the change of synovial uid parameters depends on the virulence of bacteria [12] and may be as low as 1500 leukocytes and 65% PMN which must also be considered when interpreting synovial pH testing and the sensitivity reported here.…”

Synovial fluid calprotectin performs better than synovial fluid polymerase chain reaction and interleukin-6 in the diagnosis of periprosthetic joint infection

“…For both synovial fluid PCR and synovial fluid IL6, the sensitivity of each test has remained similar, but the specificity has increased compared to the results of previous meta-analyses. 5,7 the performance characteristics of each test, as well as the results of previous meta-analyses, is summarized in table v. Further to this, a previous study by mihalič et al 45 showed that synovial fluid IL6 was not superior to cell count and differential in the detection of PJi. likelihood ratio scattergram analyses (Figure 8 and Figure 9) demonstrated synovial fluid PCR and synovial fluid IL6 to be best used as confirmatory tests.…”

Synovial fluid pH is as specific as synovial leukocyte count but less sensitive for the diagnosis of chronic prosthetic joint infection

“…For our cohort the specificity of WBC count (88%) and PMN% (98%) was as high as for pH (89%), whereas the sensitivity was best for WBC count (90%), but lower for PMN% (73%) and pH (53%). However, other institutions [ 12 ] or authors [ 25 ] recommend lower cut-off values to detect low-grade infections due to the fact, that the change of synovial fluid parameters depends on the virulence of bacteria [ 12 ] and may be as low as 1500 leukocytes and 65% PMN which must also be considered when interpreting synovial pH testing and the sensitivity reported here.…”