Leukocyte Esterase Strip Test: A Rapid and Reliable Method for the Diagnosis of Infections in Arthroplasty.

The reliability of the leukocyte esterase (LE) strip test needs further investigation. A total of 204 joints suspected of having periprosthetic joint infection were enrolled from July 2014 to June 2016. One drop of synovial fluid extracted by joint aspiration was applied to LE strips. The results were recorded after 2 to 3 minutes according to the 5 color grades on the color chart (-neg, 25, 27, 250, and 500). A centrifuge was used before the LE strip test when the synovial fluid was mixed with blood. Based on the Musculoskeletal Infection Society criteria, 88 joints were diagnosed as being infected and 116 as not infected. On positive threshold comparison (500 vs 250), there was no statistically significant difference in sensitivity (92.0% vs 97.7%, P=.0736), but specificity was significantly increased in the 500 group (93.1% vs 80.2%, P=.0003). When only 500 was considered positive, the sensitivity, specificity, positive predictive value, and negative predictive value were 92.0% (95% confidence interval [CI], 83.8%-96.5%), 93.1% (95% CI, 86.4%-96.8%), 91.0% (95% CI, 82.6%-95.8%), and 93.9% (95% CI, 87.4%-97.3%), respectively. Compared with white blood cell count, the LE strip test had similar sensitivity (93.2% vs 92.0%, P=1) and specificity (92.2% vs 93.1%, P=1). In cases using the centrifugation method, sensitivity and specificity also remained favorable. In this study, using 500 rather than 250 as the positive threshold increased accuracy. Compared with white blood cell count and polymorphonuclear neutrophil percentage, the LE strip test has excellent sensitivity and specificity and is reliable. Synovial fluid centrifugation is an effective means of overcoming interference from erythrocytes. [Orthopedics. 2018; 41(2):e189-e193.].