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Original research
Utility of bedside leucocyte esterase testing to rule out septic arthritis
  1. Thomas Knapper1,
  2. Richard J Murphy1,
  3. Brett Rocos1,
  4. James Fagg2,
  5. Nick Murray3,
  6. Michael Richard Whitehouse1,4
  1. 1 Department of Trauma and Orthopaedics, North Bristol NHS Trust, Westbury on Trym, Bristol, UK
  2. 2 Department of Trauma and Orthopaedics, Royal United Hospitals Bath NHS Foundation Trust, Bath, Bath and North East Somerset, UK
  3. 3 Trauma and Orthopaedics, Great Western Hospital, Swindon, UK
  4. 4 Musculoskeletal Research Unit, University of Bristol School of Clinical Science, Bristol, UK
  1. Correspondence to Mr Thomas Knapper, Department of Trauma and Orthopaedics, North Bristol NHS Trust, Westbury on Trym, Bristol, BS10 5NB, UK; tdknapper{at}me.com

Abstract

Introduction Suspected septic arthritis is a common presentation to EDs. The underlying diagnosis is often non-infective pathology. Differentiating between aetiologies is difficult. A bedside test with high negative predictive value (NPV) may allow safe discharge of patients, reduce the time in the ED, hospital admission and associated costs. This study aims to evaluate the NPV of bedside leucocyte esterase (LE) in the assessment of these patients.

Methods A prospective multicentre observational study of ED adult patients referred to orthopaedics with suspected native joint septic arthritis between October 2015 and April 2016. At three hospital sites in the Bristol region, the results of the LE test exposed to aspirated synovial fluid were recorded along with Gram stain, culture, haematinics and length of stay. A positive LE test was considered 2+ or 3+ leucocytes based on the test strip colour. Data were analysed to establish sensitivity, specificity, NPV and positive predictive value (PPV) against the gold standard 48-hour culture. We determined the potential number of inpatient bed-days that might be avoided using this bedside test.

Results Eighty patients underwent joint aspiration. Five cases had positive 48-hour culture. All (5/5) infected cases showed ≥2+ LE, sensitivity of 100% (95% CI 47.8% to 100%) while the Gram stain was positive in only one case (sensitivity 20%, 95% CI 0.51% to 71.6%). Twenty-three LE were read negative or 1+, all with negative 48-hour culture results, resulting in an NPV of 100% (95% CI 82.1% to 1.00%) for a negative LE test. Specificity of a positive LE test was 30.7% (95% CI 20.5% to 42.45%) with PPV of 8.77% (95% CI 7.64% to 10.1%). It was calculated that 57 orthopaedic bed-days could have potentially been saved by immediately discharging those with a negative LE test.

Conclusions LE point-of-care testing for suspected septic arthritis of native joints has a high NPV. Implementation of LE may facilitate more rapid discharge of patients with negative results. This test has the potential to reduce diagnostic uncertainty and costs to the healthcare system.

  • infection
  • musculo-skeletal
  • non traumatic problems
  • soft tissue infection
  • cost effectiveness
  • diagnosis

Data availability statement

All data relevant to the study are included in the article or uploaded as supplemental information.

http://dx.doi.org/10.1136/emermed-2020-209842

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    Data availability statement

    All data relevant to the study are included in the article or uploaded as supplemental information.

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    Footnotes

    • Handling editor David Metcalfe

    • Contributors All authors listed on the manuscript contributed substantially to both the project and production of the manuscript. TK, RJM and BR wrote the protocol with supervision from MRW. TK, RJM and BR were joint study leads at one side and NM and JF were the study leads at the other sites. All authors were responsible for data collection and processing. MRW wrote the data analysis and power calculations. All authors were involved in the writing and editing process of the manuscript and all authors have approved the final manuscript.

    • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

    • Competing interests None declared.

    • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

    • Provenance and peer review Not commissioned; externally peer reviewed.