MUNICH -- A simple breath test accurately predicts which patients with a chronic cough will benefit from inhaled corticosteroid treatment, according to a study presented here.
MUNICH, Sept. 7 -- A simple breath test accurately predicts which patients with chronic cough will benefit from inhaled corticosteroid treatment, according to a retrospective study presented here.
The exhaled nitric oxide test, used to diagnose asthma, outperformed another asthma test, the methacholine challenge, Peter Hahn, M.D., of the Mayo Clinic in Rochester, Minn., said at the European Respiratory Society meeting.
"This very accurate -- but underused -- test could be used up front for all patients complaining of chronic cough, saving significant time and expense in other testing," Dr. Hahn said. "It helps us get to the treatment and bring relief to the patient in the least invasive, fastest way possible."
The exhaled nitric oxide test, which measures inflammation in the bronchial tubes, requires patients to breath into an analyzer four or five times over about 10 minutes. Abnormally high exhaled nitric oxide levels may indicate asthma or non-asthmatic eosinophilic bronchitis.
The methacholine challenge test takes from 45 minutes to two hours and is more difficult for patients to tolerate because the test actually induces airway constriction, Dr. Hahn said.
The study retrospectively reviewed the charts of 64 patients seen at the clinic during 2004 and 2005. These patients were evaluated with both the exhaled nitric oxide test and the methacholine challenge.
Forty-one patients with high exhaled nitric oxide levels were started on inhaled corticosteroids. Of these, 28 had been diagnosed with asthma and the rest had other causes of chronic cough, which can include eosinophilic bronchitis, postnasal drip syndrome, and gastroesophageal reflux, the investigators noted.
Of these 41 patients, 36 (88%) reported improvement in their cough. The improvement was not related to any specific underlying cause of the cough, Dr. Hahn said.
The 23 patients with normal exhaled nitric oxide levels were also given inhaled corticosteroids. However, only two of these 23 patients (8.6%) reported that their coughs got better.
Further analysis failed to find a similar relationship between the methacholine challenge and response to inhaled corticosteroids. Of those with a positive test, 64% responded to the treatment. However, 52% of those with a negative test also responded.
In identifying the patients who would respond to inhaled corticosteroids, the positive predictive value of the exhaled nitric oxide test was 90% and the negative predictive value was 85%, Dr. Hahn said. In contrast, the positive predictive value of the methacholine challenge test was only 64% and the negative predictive value 48%, he said.
"As a point of service test, measurement of exhaled nitric oxide accurately predicted asthma in patients presenting for chronic cough evaluation," the investigator said "Furthermore, patients with a positive exhaled nitric oxide had a strong likelihood of response to inhaled corticosteroids whereas a negative exhaled nitric oxide virtually excluded response to inhaled corticosteroids."
The exhaled nitric oxide test likely works so well in identifying patients who will respond to inhaled cortical steroids because the test essentially measures eosinophilic airway inflammation, which is especially amenable to steroid treatment, Dr. Hahn said.
However, results of the current study should be confirmed with a prospective clinical trial, which Dr. Hahn's research group plans, he said.