Previous studies looked at a single sample to assess whether those with asthma had the white blood cell involvement, Fahy explained, while this study looked at many over time.
"This study reinforces the idea that asthma is not a one-type disease," he said.
Even within the nearly 50 percent without the white blood cell involvement, there are probably many different subtypes, Fahy noted.
The test used was a complicated research test, Fahy pointed out, and it is not easily done in clinical practice.
Based on the study results, researchers might next work on a simpler test to determine if those with asthma have involvement of these white blood cells, he said. Eventually, the findings may help doctors better individualize asthma treatment.
The findings suggest that a sizeable group of people with mild to moderate asthma have a type of disease that is not typical, with poorly understood mechanisms, and that new treatments will be needed, Fahy concluded.
"The finding that half of these had the absence of eosinophils in the sputum was a little surprising," said Dr. Len Horovitz, a pulmonary specialist at Lenox Hill Hospital in New York City.
"It's higher than I thought," Horovitz said. The "cascade" of inflammation in asthma -- what happens to bring on the symptoms -- has been well studied, he noted. However, "we can't guarantee that our current regimen of bronchodilators plus inhaled corticosteroids is going to work, even in mild asthma," Horovitz explained.
Doctors should ask their patients with asthma if they produce a lot of sputum, Horovitz suggested. If they do, they tend to respond to the corticosteroids.
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