Association among lung function, exhaled nitric oxide, and the CAN questionnaire to assess asthma control in children

The aim of this study was to investigate the association among a validated symptom-based questionnaire for asthma control in children (CAN), forced expiratory volume in 1 sec (FEV(1)), and fractional exhaled nitric oxide (FE(NO)).

Observational cross-sectional study was performed in a consecutive sample of asthmatic children aged between 7 and 14 years old from December 2007 to February 2008. FE(NO) was measured with a portable electrochemical analyzer and forced spirometry was performed according to American Thoracic Society/European Respiratory Society. The CAN questionnaire was completed by the parents (aged <9 years old) or by the children (> or = 9 years old). The strength of the association among FEV(1), FE(NO), and CAN questionnaire was studied using Spearman's rho, and the degree of agreement for asthma control among FEV(1), FE(NO), and CAN questionnaire, with classification of these variables according to values of normality, was studied using Pearson's chi(2) test and Cohen's kappa (KC).

We studied 268 children, mean age 9.7 +/- 2.1 years. Significant correlations were found between FE(NO) and CAN (r = 0.2), between FEV(1) and CAN (r = -0.3), and between FE(NO) and FEV(1) (r = -0.12). On classifying the variables according to values of normality, no agreement was found to establish the degree of asthma control between FE(NO) and CAN (KC = 0.18, chi(2) Pearson = 9.63); between FEV(1) and CAN (KC = 0.29, chi(2) = 38.5); or between FE(NO) and FEV(1) (KC = 0.07, chi(2) = 4.9).

The association among the three measurement instruments used to assess asthma control (FEV(1), FE(NO), and CAN) was weak. These are instruments that quantify variables that influence asthma in different ways, in this sense, none can be used instead of another in asthma management although they are complementary.