Diagnostic and prognostic value of serum antibodies against Pseudomonas aeruginosa in cystic fibrosis

Background: Eradication of Pseudomonas aeruginosa in patients with
cystic fibrosis (CF) is possible if initiated early in the course
of colonisation. To detect P aeruginosa as early as possible is
therefore a major goal. This study was undertaken to validate a
commercialised test for the detection of serum Pseudomonas
antibodies in patients with CF.Methods: A representative cross
sectional analysis of serum antibodies against three Pseudomonas
antigens (alkaline protease, elastase, and exotoxin A) was
performed in 183 patients with CF of mean age 16.7 years and FEV1
85.9% predicted. The results were correlated with microbiological
results from the previous 2 years to calculate sensitivity,
specificity, positive and negative predictive values. The following
2 years were assessed to determine prognostic predictive
values.Results: A combination of all three tested antibodies
yielded the best results with a sensitivity of 86%, specificity of
96%, and a positive predictive value of 97%. These values were
higher if only patients in whom sputum cultures were available were
considered (n = 76, sensitivity 95%, specificity 100%, positive
predictive value 100%). The prognostic positive predictive value
was high in intermittently infected patients (83%) but low in
patients free of infection (33%), whereas the prognostic negative
predictive value was high in patients free of infection (78%) and
low in intermittently infected patients (58%).Conclusions: Regular
determination of serum antibodies may be useful in CF patients with
negative or intermittent but not with positive P aeruginosa status.
A rise in antibody titres indicates probable infection and
eradication treatment may be initiated even in the absence of
microbiological detection of P aeruginosa.