Articular infection is an orthopedic challenge due to its difficult diagnosis and devastating results. Various diagnostic studies exist: culture, ESR, CRP, count of leukocytes, among others, but none is specific, they all take more than 30 minutes to complete, and require complex infrastructure. In this study, we determine the sensitivity and specificity of the leukocyte esterase for detection of an infectious process joint in Mexican population. During November 2015 to April 2016, we obtained synovial fluid from two groups of patients: one with a diagnosis of synovial joint infection with or without implant, and the control group, without infection but with degenerative pathology of the knee. We evaluated the sample using the leukocyte esterase test COMBI-SCREEN 11SYS with colorimetric reading at two minutes; two crosses determined positive for infection; the remainder of the sample was sent for culture. We performed the test in 64 samples of synovial fluid, 19 diagnosed with articular infection and 45 without it. We obtained a sensitivity of 100%, specificity of 88.24%, PPV of 68.42%, and NPV of 100%; Kappa index of .753. Leukocyte esterase is an effective test to detect an infectious process against an inflammatory one with a high probability of success. This study presented an index of agreement Kappa of 0.753, proving to be reproducible.