Winning Abstracts from the 2008 Medical Student Abstract Competition: Correlation Of The Asthma Control Test With Exhaled Nitric Oxide
Authors: Douglas L Nguyen, Dominique M. Brandt , Jessica Wentworth, Jonathan A.Bernstein
Clinicians typically rely on patient symptoms, spirometry, and peak expiratory flow rates to assess patient with asthma. However, fractionated exhaled nitric oxide (FENO) is becoming increasingly recognized as an important clinical tool for diagnosing and assessing asthma because it correlates well with airway inflammation, is non-invasive, easy to perform and reproducible. Our objective is to determine the utility of using the Asthma Control Test (ACT) alone or in combination with FENO in order to further improve the clinician’s ability to measure asthma control.
This study enrolled 100 patients between the ages of 18-79 with a physician-diagnosis of asthma confirmed by a 12% improvement in FEV1 post-bronchodilators. Patients were excluded if they had a diagnosis of chronic obstructive pulmonary disease and/or were active smokers. Correlation coefficients were obtained using the Spearman rho for nonparametric data and multiple regression analysis was performed using ACT as the dependant variable while controlling for medication, asthma severity, age, gender, body mass index (BMI), FENO, FEV1, FVC, and PEFR.
Population characteristics were as follows: 56% female, 45% male, 79% Caucasians, 20% African Americans and 1% Asian. The median age of the population was 50 (range 18-79 yrs) and the median FENO was 28 ppb (range 3.3-205 ppb). Seventeen patients were on oral corticosteroids (CS). The analyses were performed including and excluding the oral CS population. After excluding subjects on oral CS’s, the average FENO level correlated very well with the ACT for subjects between the ages 25 to 67 (rho= - 0.31 p=0.01) but not for subjects younger than 24 or older than 68. The ACT correlated with FEV1, FVC and PEFR regardless of age. Using a cut off of 20 ppb for average FENO and 19 for ACT, there was concordance between the FENO and ACT in 68% of subjects between the ages 25 to 67. Regression analysis of subjects in the 25-67 y/o age range revealed that the ACT results significantly interacted with FENO (p=0.07), FEV1 ( p=0.03), FVC (p=0.03), PEFR (p=0.0007) and a trend with gender (p=0.08), but not BMI , age, medications or asthma severity.
The ACT correlates well with average FENO and other lung function markers for asthma in subjects between the ages of 25 to 67 whereas poor correlation was seen in younger and older age groups. These findings suggest that optimal correlation between the average FENO levels, ACT, and lung function may be age dependent. These results also emphasize that FENO is a useful biomarker for identifying asymptomatic patients with poorly controlled asthma.
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