Nigrovic LE, Bennett JE, Balamuth F, et al. - Among children with acute arthritis undergoing evaluation for Lyme disease presenting to a participating Pedi Lyme Net emergency department (2015–2019), a C6 enzyme immunoassay (EIA) test was performed to determine the role of this test in guiding initial management of these patients. Lyme arthritis was defined with a positive or equivocal C6 EIA test result followed by a positive supplemental immunoblot result and septic arthritis was defined as a positive synovial fluid culture result or a positive blood culture result with synovial fluid pleocytosis. Researchers here studied 911 patients; of these, 211 children (23.2%) had Lyme arthritis, 11 (1.2%) had septic arthritis, and 689 (75.6%) had other inflammatory arthritis. For Lyme arthritis, a positive or equivocal C6 EIA result was identified to have 100% sensitivity (211 out of 211; 95% confidence interval [CI]: 98.2%–100%) and 94.2% specificity (661 out of 700; 95% CI: 92.5%–95.9%). These findings support the possible utility of a C6 EIA result in guiding initial clinical decision-making, without misclassifying children with septic arthritis in Lyme disease endemic areas.