Multi-centre evaluation of Gram stain in the diagnosis of septic arthritis

<b>Introduction</b>: Gram stain of synovial fluid is a rapid test for the diagnosis of native joint septic arthritis. Single-centre studies have suggested Gram stain will miss a considerable proportion of patients who are subsequently synovial-fluid-culture-positive or polymerase chain reaction (PCR)-positive. The object of this study was to reassess Gram stain in a large, multi-centre cohort of patients from the United Kingdom (UK) and Ireland. <b>Methods</b>: The study was a retrospective analysis combining two large datasets. We defined septic arthritis microbiologically as at least one positive joint aspirate culture and/or PCR test. "Best case" and "worst case" definitions were applied depending on the likelihood organisms were true infecting pathogens. <b>Results</b>: Gram stain missed a high proportion of culture-/PCR-positive patients using both the best (74 % missed) and worst (81 % missed) case definitions. Using the best case definition, the sensitivity of Gram stain was 0.26, specificity 0.99, positive predictive value 0.84, negative predictive value 0.87, accuracy 0.87, and area under the receiver operator curve 0.62 (95 % CI 0.57 to 0.68, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>p</mml:mi> <mml:mo><</mml:mo> <mml:mn>0.001</mml:mn></mml:mrow> </mml:math> ). False positive Gram stains were infrequent (1 %). Age, joint involved, and other synovial fluid characteristics were less predictive of a positive culture/PCR than Gram stain. <b>Conclusions</b>: While a positive synovial fluid Gram stain should always be considered to indicate potential septic arthritis, a negative Gram stain, regardless of synovial fluid crystals or white cell count, should not be used to rule out septic arthritis. The value of Gram stain as an urgent out-of-hours test for septic arthritis is open to considerable debate.

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Publication Details

Journal
Journal of Bone and Joint Infection
Published
2025-03-17
DOI
https://doi.org/10.5194/jbji-10-61-2025
Citations
2
Primary Topic
Orthopedic Infections and Treatments
Type
article
Field-Weighted Citation Impact
4.01
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article

Multi-centre evaluation of Gram stain in the diagnosis of septic arthritis

Gwennan Jones, Teresa Peach, Kordo Saeed, Catherine Aldridge et al.
2 citations
Journal of Bone and Joint Infection
Orthopedic Infections and Treatments
4.01
article

Multi-centre evaluation of Gram stain in the diagnosis of septic arthritis

Gwennan Jones, Teresa Peach, Kordo Saeed, Catherine Aldridge, Lynn Moffat, Luke S. P. Moore, Sara E. Boyd, Hemant Sharma, Ben Talbot, Shaan Ashk O’Shea, Charlotte Smith, Rachel Annett, Robert Maloney, Niamh Reidy, Lucinda Barrett, Nusreen Ahmad-Saeed, Christina Petridou, Laura Leach, Shanine Mitchell, Gavin Barlow, Deepa Nayar, Michael E. Murphy, Harriet Hughes, Peter Davies, Maureen Lynch, Martin Marsh, Deborah Wearmouth
article en
2 citations

Abstract

<b>Introduction</b>: Gram stain of synovial fluid is a rapid test for the diagnosis of native joint septic arthritis. Single-centre studies have suggested Gram stain will miss a considerable proportion of patients who are subsequently synovial-fluid-culture-positive or polymerase chain reaction (PCR)-positive. The object of this study was to reassess Gram stain in a large, multi-centre cohort of patients from the United Kingdom (UK) and Ireland. <b>Methods</b>: The study was a retrospective analysis combining two large datasets. We defined septic arthritis microbiologically as at least one positive joint aspirate culture and/or PCR test. "Best case" and "worst case" definitions were applied depending on the likelihood organisms were true infecting pathogens. <b>Results</b>: Gram stain missed a high proportion of culture-/PCR-positive patients using both the best (74 % missed) and worst (81 % missed) case definitions. Using the best case definition, the sensitivity of Gram stain was 0.26, specificity 0.99, positive predictive value 0.84, negative predictive value 0.87, accuracy 0.87, and area under the receiver operator curve 0.62 (95 % CI 0.57 to 0.68, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>p</mml:mi> <mml:mo><</mml:mo> <mml:mn>0.001</mml:mn></mml:mrow> </mml:math> ). False positive Gram stains were infrequent (1 %). Age, joint involved, and other synovial fluid characteristics were less predictive of a positive culture/PCR than Gram stain. <b>Conclusions</b>: While a positive synovial fluid Gram stain should always be considered to indicate potential septic arthritis, a negative Gram stain, regardless of synovial fluid crystals or white cell count, should not be used to rule out septic arthritis. The value of Gram stain as an urgent out-of-hours test for septic arthritis is open to considerable debate.

Journal of Bone and Joint InfectionVol. 10(2)
St George's Hospital (GB), University of Liverpool (GB), Imperial College Healthcare NHS Trust (GB), University of Hull (GB), Chelsea and Westminster Hospital NHS Foundation Trust (GB), NHS Greater Glasgow and Clyde (GB), Glasgow Royal Infirmary (GB), University Hospital of Wales (GB), St George’s University Hospitals NHS Foundation Trust (GB), Newcastle upon Tyne Hospitals NHS Foundation Trust (GB), University Hospital Southampton NHS Foundation Trust (GB), Mater Misericordiae University Hospital (IE), Hampshire Hospitals NHS Foundation Trust (GB), National Institute for Health and Care Research (GB), Public Health Wales (GB), North West London Pathology (GB), University Hospital Llandough (GB), Oxford University Hospitals NHS Trust (GB), Sheffield Health and Social Care NHS Foundation Trust (GB), University of Southampton (GB), Imperial College London (GB), University of York (GB), Hull York Medical School (GB), University of Glasgow (GB)
Openalex Percentile: Top 8%
Orthopedic Infections and Treatments
4.01
DOIOpen Access PDFOpenAlex
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