Summer Season May Influence Asthma Test Results

NEW YORK (Reuters Health) - People who undergo exercise tests to help diagnose asthma may get different results depending on the season in which the test is conducted, new study findings suggest.

Exercise tests conducted in the summer, when asthma flare-ups are generally less frequent, seem to be less likely to confirm an asthma diagnosis than tests conducted in other seasons.

"This study shows that the percentage of positive exercise challenge test results in the summer is half that of any other season," write Dr. Shmuel Goldberg and colleagues, at Shaare Zedek Medical Center in Jerusalem, in the medical journal Chest.

"The major point is that patients with exercise induced asthma might have a normal exercise test if checked when their asthma is not active," Goldberg told Reuters Health. "Exercise challenge test for asthma should be done during seasons with active symptoms," the researcher added.

Other researchers have also reported an association between exercise test results and the seasons in which the tests were conducted, but those reports were all based on exercise tests that were conducted outdoors. In those instances, cold temperatures and other environmental factors could have accounted for the higher proportion of positive test results during the winter months, Goldberg's report indicates.

Goldberg and colleagues consequently evaluated the results of treadmill tests conducted in a laboratory, under constant temperature and humidity. Their study involved 532 potential military recruits, each 17 years old, who participated in exercise tests for suspected asthma.

Overall, more than one in four (26 percent) of the study participants tested positive for asthma after exercising, as measured by a 10 percent or greater drop in lung function, the researchers report.

Only about 13 percent of the group tested positive in the summer months of July to September, however, compared with a positive results rate of 29-31 percent during the rest of the year.

According to previous research, the severity of asthma symptoms is also season dependent, with various studies showing that the highest number of asthma-related visits to the emergency department occurs in the fall or winter seasons and the fewest occur in the summer. This is possibly due to the lower prevalence of asthma triggers, including low temperature and air pollutants during the summer months, the current report indicates.

"Thus, the relative absence of asthma triggers during the summer produces less asthma activity during this season, and consequently, lower sensitivity of exercise testing," Goldberg and colleagues write.

Based on the current findings, Goldberg offers this advice for patients with suspected exercise-induced asthma: "If they had their symptoms during the time the test was done - even if it was done in the summer - there is no value repeating a negative test. If, however, they are free of symptoms during the summer, a negative exercise test done in the summer should be repeated in another season when they are symptomatic."

SOURCE: Chest, October 2005