[Diagnostic value of exhaled nitric oxide measurement in mild asthma].

OBJECTIVES

To assess the diagnostic value of fractional exhaled nitric oxide (FE(NO)) in mild asthma.

MATERIAL AND METHODS

Cross-sectional descriptive study in a group of patients with no history of respiratory or allergic illness (control group) and a group of patients with a history of mild asthma with no baseline treatment (asthma group), both aged 6 to 14 years. The following examinations were performed: measurement of FE(NO) using the portable NIOX MINO(®) device, allergy tests and spirometry. Repeatability of paired FE(NO) measurements was estimated with the intraclass correlation coefficient, the repeatability coefficient and the variation coefficient. The diagnostic value was assessed with the sensitivity, specificity, area under the ROC curve and positive likelihood ratio (LR+) for each cut-off point.

RESULTS

Eighty-seven patients were included in the control group and 57 in the asthma group. The mean FE(NO) value was 12.1 ppb (SD 13.5) in the control group and 42.9 ppb (SD 24.5) in asthmatics (P<.001). The intraclass correlation coefficient was 0.98 (95% CI: 0.96-0.99) and of 0.97 (95% CI: 0.92-0.99) in controls and asthmatics, respectively. The repeatability coefficient was 5.5 in controls and 9.2 in asthmatic children, and the median variation coefficient was 8.3% and 6.1%. The optimal cut-off value for FE(NO) was 19 ppb (sensitivity and specificity were 91.4% and 87.2%, respectively). The area under the ROC curve was 0.93 (95% CI: 0.88-0.97) (P<.001) and the LR+ was 7.1. Subclinical sensitisation to pneumoallergens accounted for most false positive cases.

CONCLUSIONS

The determination of FE(NO) with NIOX MINO(®) has an adequate repeatability, especially for healthy patients. For asthmatic patients we recommend determining the average of two measurements. The test has a high diagnostic value in mild asthma. Subclinical sensitisation to pneumoallergens can cause the FE(NO) value to rise to pathologic levels.