Combination of Serologic Tests and Sputum Culture Results as the Best Diagnostic Method of Pseudomonas aeruginosa Infection in Cystic Fibrosis Patients.

Background: One of the most common reasons for mortality in patients with cystic fibrosis (CF) is lung infections, among which Pseudomonas aeruginosa (Pa) infection has the largest share. Diagnosis of Pa can be assessed by various methods such as sputum culture results and IgG antibody level via measuring the specific anti-Pa antibodies. This study aimed to select the best predictive technique in the diagnosis of Pa in CF patients through spirometry, sputum culture, and serum IgG antibody levels.

Materials and methods: In this cross-sectional study, blood and sputum or pharyngeal samples were taken from 68 patients with cystic fibrosis. Because spirometry was not possible in all patients, 34 patients could do the spirometry. The samples were studied concerning Pa infection. The data including variables such as age, sex, and spirometry results were obtained. Then, in the serologic method, 3 serum-specific antibody levels were determined by enzyme-linked immune sorbent assay (ELISA).

Results: The average age of children was 7.4 ± 5.6 (ranging from 0.5 to 23) years. Generally, the percentage of Pa infection increased in CF patients with higher ages. A statistically direct significant relationship was observed between the concentration of serum IgG antibodies in patients with CF and Pa-positive sputum culture results (p<0.05).

Conclusion: Serum IgG antibodies against specific Pa antigens could be a diagnostic method against Pa infection, especially in patients who cannot expectorate. However, because of the positive and negative predictive value of both serum IgG antibody levels and the results of the sputum culture, we suggested that utilizing the combination of these methods could be beneficial in earlier diagnosis of Pa.