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


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.



  • Catherine H, Martin OW, Philip W. Urinary antigen testing for pneumococcal pneumonia: is there evidence to make its use uncommon in clinical practice? ERJ Open Res 2020;6:00223–2019.
  • Song JY, Eun BW, Nahm MH. Diagnosis of pneumococcal pneumonia: current pitfalls and the way forward. Infect Chemother 2013;45:351–66. doi: 10.3947/ic.2013.45.4.351.
  • Takahashi S, Ishitsuka T, Namatame K, Nakamura M. A false-positive pneumococcal rapid urinary antigen test in Streptococcus intermedius infection. Respirol Case Rep 2019;7:e00466. doi: 10.1002/rcr2.466.
  • Slotved HC, Jørgensen CS, Jørgensen KM, Fuursted K. A case of false-positive pneumococcal urinary antigen test in a bacteremic Streptococcus agalactiae infection. APMIS 2020;128:511–12. doi: 10.1111/apm.13066.
  • Andreo F, Prat C, Ruiz-Manzano J, Lores L, Blanco S, Cuesta MA, et al. Persistence ofStreptococcus pneumoniae urinary antigen excretion after pneumococcal pneumonia. Eur J Clin Microbiol Infect Dis 2009;28:197–201. doi: 10.1007/s10096-008-0606-3.
  • Smith MD, Derrington P, Evans R, Creek M, Morris R, Dance DAB, et al. Rapid diagnosis of bacteremic pneumococcal infections in adults by using the Binax NOW Streptococcus pneumoniae urinary antigen test: a prospective, controlled clinical evaluation. J Clin Microbiol 2003;41:2810–13. doi: 10.1128/JCM.41.7.2810-2813.2003.
  • Sordé R, Falcó V, Lowak M, Domingo E, Ferrer A, Burgos J, et al. Current and potential usefulness of pneumococcal urinary antigen detection in hospitalized patients with community-acquired pneumonia to guide antimicrobial therapy. Arch Intern Med 2011;171:166–72. doi: 10.1001/archinternmed.2010.347.
  • Metlay JP, Waterer GW, Long AC, Anzueto A, Brozek J, Crothers K, et al. Diagnosis and treatment of adults with community-acquired pneumonia. An official clinical practice guideline of the American Thoracic Society and Infectious Diseases Society of America. Am J Respir Crit Care Med 2019;200:e45–e67. doi: 10.1164/rccm.201908-1581ST.
  • The Japanese Respiratory Society. Guidelines for the management of pneumonia in adults [in Japanese]. Tokyo: The Japanese Respiratory Society; 2017, pp. 76–8.
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    Published: 2022-02-14
    Issue: 2022: Vol 9 No 2 (view)

    How to cite:
    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.

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