Comparison of exhaled nitric oxide measurement with conventional tests in steroid-naive asthma patients

Nitric oxide (NO) is a molecule with potent biological activity that plays an important role in the physiology of the respiratory system. Increased expression of inducible nitric oxide synthase (iNOS) and elevated fractional concentration of exhaled nitric oxide (F(ENO)) are seen in asthmatic patients. Measurement of F(ENO) has become increasingly recognized for use in the evaluation of bronchial inflammation during monitoring of antiinflammatory treatment.

The aim of this study was to evaluate F(ENO) in a group of steroid-naive asthmatics and assess the relationship of this parameter with the results of other tests used in the diagnosis of asthma and monitoring of antiinflammatory treatment in asthmatic patients.

The study was conducted in a group of 101 steroid-naive asthmatics (56 allergic and 45 nonallergic) and 39 healthy volunteers. All patients underwent measurement of F(ENO), skin prick tests with common inhaled allergens, analysis of serum eosinophil cationic protein (ECP) and blood eosinophilia, and flow-volume spirometry. When the forced expiratory volume in the first second (FEV1) was less than 80% of predicted, reversibility of airway obstruction with a beta2-agonist was assessed. A nonspecific bronchial provocation test with histamine was carried out in asthmatic patients with a baseline FEV1 of more than 70% of predicted.

Compared to the healthy volunteers, F(ENO) was elevated in both groups of asthmatics. F(ENO) in the allergic asthma group was higher than in the group of nonallergic asthmatics. In allergic and nonallergic asthmatics, F(ENO) was significantly correlated with bronchial hyperresponsiveness to histamine, reversibility of airway obstruction, serum ECP levels, and blood eosinophilia. F(ENO) did not correlate with baseline FEV, in either group of asthmatics. In 31% of nonallergic and 9% of allergic patients, F(ENO) was less than 20 parts per billion.

We suggest that measurement of F(ENO) could be clinically useful in steroid-naive asthmatics and should be more widely used in clinical practice. Measurement of F(ENO) is a noninvasive, simple, and reproducible procedure, the results of which correlate with other routinely used methods in the diagnosis of asthma. However, it is worth noting that some patients, especially those with nonallergic asthma, do not display elevated F(ENO).