Leukocyte Esterase Testing Of Synovial Fluid For Septic Joint In A Community Setting: A Case Series

Abstract

PURPOSE: Septic arthritis, bacterial infection of the joint space, is an orthopedic emergency and requires prompt antibiotics and joint decompression with irrigation and drainage. Poor sensitivity characterizes current testing available to the Emergency Clinician, including systemic leukocytosis (50%), blood culture (25-50%) gram stain (30% to 70%) and synovial leukocytosis of 50,000 (70%). Recently, orthopedic research has begun to explore utilization of leukocyte esterase assays as an additional investigation for septic arthritis. No previous study has examined the utility and feasibility of leukocyte esterase in a community Emergency Department. METHODS: In this prospective study, patients who underwent joint aspiration with joint fluid culture underwent synovial leukocyte esterase testing. Diagnosis of septic arthritis was confirmed if one of the following is found: 1) a positive synovial fluid culture; 2) pathogen isolated from blood culture and clinical presentation deemed consistent with septic arthritis; or 3) turbid synovial fluid with a negative crystal analysis result. RESULTS: 23 joint aspirations were performed from March through December of 2020, of which 5 were diagnosed with septic arthritis. 4 had readable leukocyte esterase tests and all 4 resulted in positive tests, indicating sensitivity of 100%. The fifth was unreadable due to excess blood in the sample. Of the remaining 18 samples, 16 were readable and 6 had a positive leukocyte esterase, indicating specificity of 63%. Notably, synovial leukocytosis demonstrated sensitivity of 25% and specificity of 86% and Gram stain demonstrated sensitivity of 60% and specificity of 100%. CONCLUSIONS: This study suggests that synovial fluid leukocyte esterase is an effective tool in the hands of the Emergency Clinician that, when readable, has superior sensitivity for septic joint than other testing available based on both results from this study and from existing literature. This case series also demonstrates pathologies besides septic joint that resulted positive leukocyte esterase test and the ease with which this test was implemented in a community emergency department. Given these results and its cost-effectiveness (roughly 50¢), this study demonstrates potential for more widespread use of synovial leukocyte esterase testing.