Brief Report Utility of point-of-care synovial lactate to identify septic arthritis in the emergency department Eileen Shu, Leyla Farshidpour, Megann Young, Michael Darracq, Crystal Ives Tallman ⁎ UCSF Fresno Department of Emergency Medicine, United States of America abstract article info Article history: Received 1 December 2018 Received in revised form 16 December 2018 Accepted 17 December 2018 Background: Synovial lactate is a promising biomarker to distinguish septic from aseptic arthritis. If available as a point-of care test, synovial lactate would be rapidly available to aid the emergency provider in clinical decision making. This study assesses the test characteristics of synovial lactate obtained using an EPOC© point-of-care (POC) analyzer to rapidly distinguish septic from aseptic arthritis in the emergency department. Methods: We enrolled a convenience sample of patients with possible septic arthritis presenting to the emer- gency department at a large urban academic center between October 2016 and April 2018. Enrolled patients underwent arthrocentesis based on the clinical judgment of the treating provider. We obtained synovial lactate levels (SLL) from the POC device. Standard laboratory analysis, synovial fluid culture, emergency and hospital course, operative procedures, antibiotics, and discharge diagnosis were abstracted from the electronic medical record. Results: Thirty-nine patients undergoing forty separate arthrocentesis procedures were enrolled in this study over the two-year period. The sensitivity and specificity of SLL ≥ 5 mmol/L was 0.55 and 0.76 respectively, with +LR 2.3 and -LR 0.6. The sensitivity and specificity of SLL ≥ 10 mmol/L was 0.27 and 0.97 respectively, with +LR 7.9 and -LR 0.8; SLL ≥ 10 mmol/L performed similarly to overall synovial WBC ≥ 50,000/μL by conven- tional laboratory testing. Conclusion: It is feasible to obtain a synovial lactate level using the EPOC© POC device. In our study, POC SLL per- forms similarly to other markers used to diagnose septic arthritis. Further study with larger sample sizes is warranted. © 2018 Published by Elsevier Inc. 1. Introduction Septic arthritis remains a relatively rare diagnosis, with roughly 16,000 cases seen in the Emergency Department (ED) per year, or 0.01% of annual ED visits in the United States [1]. It is difficult to distin- guish septic from aseptic arthritis, since both frequently present with a similar clinical picture. Prior research suggests that physicians are able to accurately diagnose the etiology of acute non-traumatic monoarticular arthritis at approximately 3 days [2]. ED physicians do not have the luxury of this timeline, and inadequate or delayed treat- ment of septic arthritis can lead not only to increased morbidity from joint destruction in up to 50% of cases [3], but also to mortality in N10% of cases [4]. Classic signs and symptoms of septic arthritis, such as non-traumatic acute monoarticular joint pain, swelling, erythema, or micromotion ten- derness to palpation, are not sufficiently sensitive nor specific for the di- agnosis of septic arthritis [5]. Adding to the complexity of making an accurate diagnosis, there is not a clear diagnostic gold standard [4,6,7], with case definitions based on one of four criteria: (1) isolation of path- ogenic organism from affected joint, (2) isolation of pathogenic organ- ism from another source (i.e. blood) in the context of a suspicion of joint infection, (3) typical clinical features and turbid joint fluid in joint previously treated with antibiotics, or (4) postmortem features suspicious of septic arthritis [4]. Because synovial fluid culture is only 75–95% sensitive for septic arthritis [8], and time to culture limits time- liness of diagnosis, accurate and fast diagnostic laboratory markers are necessary to identify septic arthritis. Though laboratory markers such as C-reactive protein (CRP) and pe- ripheral white blood cell count (pWBC) have been used to distinguish between the two types of arthritis, several studies have shown that these markers do not differ significantly between septic and aseptic joints [9,10]. The classically taught synovial WBC (sWBC) ≥ 50,000/μL also does not adequately distinguish between these two disease pro- cesses [4,11]. Other biomarkers, such as laboratory-measured synovial American Journal of Emergency Medicine 37 (2019) 502–505 ⁎ Corresponding author at: Department of Emergency Medicine, UCSF Fresno Center for Medical Education and Research, 155 N Fresno St, Fresno, CA 93701, United States of America. E-mail addresses: leylazakeri@mail.fresnostate.edu (L. Farshidpour), myoung@fresno.ucsf.edu (M. Young), Mdarracq@fresno.ucsf.edu (M. Darracq), civestallman@fresno.ucsf.edu (C. Ives Tallman). https://doi.org/10.1016/j.ajem.2018.12.030 0735-6757/© 2018 Published by Elsevier Inc. Contents lists available at ScienceDirect American Journal of Emergency Medicine journal homepage: www.elsevier.com/locate/ajem