Open AccessMisdiagnosis Due to False-Positive Detection of Pneumococcal Urinary Antigen
Author(s) -
Kaori Notomi,
Taku Harada,
Takashi Watari,
Juichi Hiroshige,
Taro Shimizu
Publication year - 2022
Publication title -
european journal of case reports in internal medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.125
H-Index - 1
ISSN - 2284-2594
DOI - 10.12890/2022_003198
Subject(s) - medicine , streptococcus pneumoniae , pneumonia , urinary system , antigen , false positive paradox , gastroenterology , immunology , pathology , antibiotics , microbiology and biotechnology , biology , machine learning , computer science
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.