Evaluation of a rapid lateral flow calprotectin test for the diagnosis of prosthetic joint infection
AbstractBackgroundMicrobiological diagnosis of prosthetic joint infection (PJI) relies on culture techniques that are slow and insensitive. Rapid tests are urgently required to improve patient management. Calprotectin is a neutrophil biomarker of inflammation that has been demonstrated to be effective for the diagnosis of PJI. A calprotectin based lateral flow test has been developed for the rapid detection of PJI using synovial fluid samples.MethodsA convenience series of 69 synovial fluid samples from patients at the Norfolk and Norwich University Hospitals (NNUH) were collected intraoperatively from 52 hip and 17 knee revision operations. Calprotectin levels were measured using a new commercially available lateral flow assay for PJI diagnosis (Lyfstone). For all samples, synovial fluid was pipetted onto the lateral flow device and the signal was read using a mobile phone app after 15 minutes incubation at room temperature.ResultsAccording to the Musculoskeletal Infection Society (MSIS) criteria, 24 patients were defined as PJI positive and the remaining 45 were negative. The overall accuracy of the lateral flow test against the MSIS criteria was 75%. The test had a sensitivity and specificity of 75% and 76% respectively with a positive predictive value (PPV) of 62% and a negative predictive value (NPV) of 85%. Discordant results were then reviewed by the clinical team using available patient data to develop an alternative gold standard for defining presence/absence of infection (MSIS+). Compared to MSIS+, the test showed an overall accuracy of 83%, sensitivity and specificity of 95% and 78% respectively, a PPV of 62% and an NPV of 98%. Test accuracy for hip revisions was 77% and for knee revisions was 100%.ConclusionsThis study demonstrates that the calprotectin lateral flow assay is an effective diagnostic test for PJI. Our data suggests that the test is likely to generate false positive results in patients with metallosis and gross osteolysis.