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Diagnostic value of serological tests against Pseudomonas aeruginosa in a large cystic fibrosis population

¹ CF-Centre Utrecht, University Medical Centre, Utrecht, The Netherlands
² Department of Infectious Diseases, Wilhelmina Children’s Hospital, University Medical Centre, Utrecht, The Netherlands

Correspondence to:
Correspondence to:
Dr T F W Wolfs
Department of Infectious Diseases, Wilhelmina Children’s Hospital, P O Box 85090, 3508 AB Utrecht, The Netherlands; t.wolfs{at}umcutrecht.nl

Background: Serological methods to monitor Pseudomonas aeruginosa colonisation in patients with cystic fibrosis (CF) are advocated but the diagnostic value of a commercially available P aeruginosa antibody test to detect early and chronic P aeruginosa colonisation in a non-research setting has not been assessed.

Methods: Colonisation with P aeruginosa was estimated by regular culture of sputum or oropharyngeal swabs during three consecutive years in 220 patients with CF aged 0–65 years. Commercially available ELISA tests with three P aeruginosa antigens (elastase, exotoxin A, alkaline protease) were performed at the end of the study period. In a subgroup of 57 patients (aged 4–14 years) serological tests were performed annually.

Results: Using culture as the reference standard, the ELISA tests using the advised cut off values had a sensitivity of 79% and a specificity of 89% for chronic colonisation. Receiver-operator characteristic curves were created to optimise cut off values. Applying these new cut off values resulted in a sensitivity of 96% and a specificity of 79%. All three individual serological tests discriminated well between the absence and presence of chronic P aeruginosa colonisation. The sensitivity of the individual antibody test was 87% for elastase, 79% for exotoxin A, and 76% for alkaline protease. First colonisation was preceded by positive serological results in only five of 13 patients (38%).

Conclusion: In patients with CF, serological tests using specific antigens are sensitive for diagnosing chronic P aeruginosa colonisation. However, the failure of serological tests to detect early colonisation in young patients emphasises the need for continued reliance on cultures.

Abbreviations: CF, cystic fibrosis; ELISA, enzyme linked immunoassay; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity

Keywords: Pseudomonas aeruginosa; cystic fibrosis; serology; serum antibodies; prognostic value

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