Misdiagnosis Due to False-Positive Detection of Pneumococcal Urinary Antigen

  • Kaori Notomi Division of General Medicine, Showa Medical University Hospital, Tokyo, Japan
  • Taku Harada Division of General Medicine, Showa Medical University Hospital, Tokyo, Japan; Department of Diagnostic and Generalist Medicine, Dokkyo Medical University Hospital, Tochigi, Japan
  • Takashi Watari General Medicine Centre, Shimane University Hospital, Shimane, Japan
  • Juichi Hiroshige Division of General Medicine, Showa Medical University Hospital, Tokyo, Japan
  • Taro Shimizu General Medicine Centre, Shimane University Hospital, Shimane, Japan

Abstract

Introduction: The detection of pneumococcal antigens in urine is an alternative to gram staining, and their culture is central to the diagnosis of pneumococcal pneumonia. We present a case of the false-positive detection of urinary Streptococcus species pneumococcal antigen with a BinaxNOW test. This resulted in delayed diagnosis of a liver abscess.

Case description: A 70-year-old woman presented to the emergency department with a 1-day history of chills and difficulty walking. She had a fever and her physical examination was normal. Non-contrast chest computed tomography (CT) revealed a slight ground-glass opacity in the left lower lobe. Laboratory tests revealed liver injury and elevated C-reactive protein levels. A urinary pneumococcal antigen test was positive, and she was diagnosed with acute bronchopneumonia caused by Streptococcus pneumoniae. She was treated with ceftriaxone. However, abdominal contrast-enhanced CT performed the next day revealed portal vein thrombus and a left lobe liver abscess. Streptococcus constellatus was detected in a puncture specimen of the liver abscess. It was concluded that the positive urinary pneumococcal antigen test was a false-positive owing to Streptococcus infection.

Discussion: False-positive results might be explained by the presence of C-polysaccharide antigens in the cell wall of S. pneumoniae. The positive urinary antigen test together with the finding of slight ground-glass opacity in the left lung on chest CT initially led to misdiagnosis. False positives may result in misdiagnosis and unnecessary antimicrobial therapy.

Conclusion: The overuse of the pneumococcal urinary antigen tests can lead to false positives and misdiagnosis.

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  • Published: 2022-02-14

    Issue: 2022: Vol 9 No 2 (view)

    Section: Articles

    How to cite:
    1.
    Notomi K, Harada T, Watari T, Hiroshige J, Shimizu T. Misdiagnosis Due to False-Positive Detection of Pneumococcal Urinary Antigen . EJCRIM 2022;9 doi:10.12890/2022_003198.