By contrast, having airway hyperresponsiveness to both histamine (a direct bronchoconstric-tor) and mannitol was a clear predictor for failure of ICS reduction. In the present study, the responsiveness to a direct bronchoconstrictor agent was not determined, and so the relevance of this factor in our patients cannot be ascertained; however, the results of our study suggest that a decrease in PC20 of at least one doubling concentration 2 weeks after the dose of ICS was halved is a predictor of borderline significance for failure of ICS reduction. Furthermore, when measured longitudinally, the changes in PC20, but not the changes in ENO, correlated significantly with changes in either symptoms or albuterol use. These findings provide additional support for the use of AMP measurements as a tool in the assessment of asthma control. Thus, although additional studies involving a larger number of patients are necessary to confirm the utility of the changes in PC20 for predicting failure of ICS reduction, our findings suggest that changes in PC20 following the reduction of ICS may potentially provide an information more useful for predicting loss of control than did single measurements at baseline.
A number of investigators have sought to evaluate the role of ENO in assessing long-term asthma control. The usefulness of ENO in asthmatic patients treated with ICS is supported by Stirling, who found higher concentrations of ENO in patients with greater asthma severity irrespective of steroid use. In contrast, several studies have demonstrated that a single baseline assessment of ENO had a low power to predict asthma deterioration during the reduction of ICS treatment.
Table 4 —Correlations Between the Changes in PC20 or ENO Levels and the Changes in Clinical Manifestations and Pulmonary Function
| Variables | PC20 | ENO | ||
| 1
Correlation |
1 1
p Value Correlation |
1
p Value |
||
| Daytime symptom | – 0.41 | 0.02 | 0.04 | 0.79 |
| score | ||||
| Nighttime symptom | – 0.30 | 0.08 | 0.05 | 0.77 |
| score | ||||
| Albuterol use | – 0.43 | 0.009 | 0.11 | 0.91 |
| FEV1 | 0.16 | 0.36 | 0.13 | 0.92 |
| Morning PEF | 0.02 | 0.97 | – 0.02 | 0.98 |
| Evening PEF | – 0.17 | 0.33 | – 0.05 | 0.98 |
| ENO | – 0.03 | 0.87 | ||
Although our results confirm that a single baseline assessment of ENO is not useful to predict the evolution of asthma following the reduction of ICS dose, they clearly suggest that the concomitant determination of ENO and PC20 at baseline provides a relevant information to predict the success or failure of ICS reduction.
It has been suggested in the literature that changes in ENO measured over time have higher predictive value for exacerbations following ICS reduction than do single measurements.