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


CONCLUSIONS
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.
Tramper-Stranders
G A
GA
CF-Centre Utrecht, University Medical Centre, Utrecht, The Netherlands.
van der Ent
C K
CK
Slieker
M G
MG
Terheggen-Lagro
S W J
SW
Teding van Berkhout
F
F
Kimpen
J L L
JL
Wolfs
T F W
TF
D000328:Adult; D000368:Aged; D000907:Antibodies, Bacterial / Q000097:blood*; D000942:Antigens, Bacterial; D003550:Cystic Fibrosis / Q000382:microbiology*; D004797:Enzyme-Linked Immunosorbent Assay / Q000592:standards; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011552:Pseudomonas Infections / Q000175:diagnosis*; D011550:Pseudomonas aeruginosa / Q000276:immunology*; D012372:ROC Curve; D012015:Reference Standards; D012680:Sensitivity and Specificity
D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial