Evaluation of leukocyte esterase strip test for diagnosis of periprosthetic joint infection

Objective To investigate the value of leukocyte esterase (LE) strips in the diagnosis of periprosthetic joint infection (PJI). Methods From October 2014 to July 2015, 63 patients with PJI who had undergone joint puncture after arthoplasty in our hospital were enrolled in this trial. Every drop of synovial fluid was placed onto the leukocyte esterase (LE) strip (Combur¹⁰Test^®M Roche and AUTION Sticks 10PA arkray), and the results were observed after 2-3 min. If the color turned to dark violet, we recognized this as a positive result, while other colors were regarded as negative results. The centrifuge was used when the synovial fluid was mixed with blood before being placed onto the LE strip. At the same time, the diagnostic criteria of Muscularskeletal Infection Society (MSIS) were used to identify whether periprosthetic joint infection was found in patients or not. The results of diagnosis and LE strips test were compared, and the sensitivity, specificity, positive predictive value, negative predictive value were calculated. Results For all 63 patients, 35 cases were diagnosed as PJI and 28 cases were not infected by MSIS criteria. Two types of LE strip presented the same results with sensitivity of 91.4% (95% CI: 75.8%-97.8%), specificity of 96.4% (95% CI: 79.8%-99.8%), positive predictive value of 97.0% (95% CI: 82.5%-99.8%) and negative predictive value of 90.0% (95% CI: 72.3%-97.4%). One false positive case and three false negative cases were in this trial. Conclusion There is a high sensitivity and specificity in the diagnosis of periprosthetic joint infection by LE strip which is simple and cost-saving. Though two types of LE strips indicate the same results, the Roche strip is inconvenient for color-reading by naked-eyes directly with thick filter membrane.