TUESDAY, May 24, 2005 (HealthDay News) -- Within a few years, doctors may have a new tool to help assess the severity of your asthma, which will help them better predict your need for inhaled corticosteroid medication.
That tool is a machine that measures exhaled nitric oxide. The amount of nitric oxide in exhaled air is a marker of asthma, and higher levels of nitric oxide indicate worsening asthma, according to a study in the May 26 issue of the New England Journal of Medicine.
After comparing a group of asthma patients assessed using standard measurements, such as the patient's reporting of symptoms and peak flow measurements, to a group assessed using exhaled nitric oxide measurements, the researchers were able to reduce the amount of inhaled corticosteroids by an average of 40 percent.
"Nitric oxide measurements are a major step forward in assessing asthma," said study co-author Dr. D. Robin Taylor, a professor of respiratory medicine at the Dunedin School of Medicine, in New Zealand.
"The most important lesson [from this study] is that the overall control of asthma can be well maintained, despite using a much lower dose of inhaled steroid. Nitric oxide measurements allowed the dose to be adjusted safely and appropriately," Taylor said.
Asthma affects about 27 million Americans, according to an editorial in the same issue of the journal. While treatments for asthma have advanced significantly, it isn't always easy for doctors to know how much medication a patient needs. Too little and serious asthma exacerbations can result; too much and the asthma may be controlled, but the patient may experience unnecessary side effects.
"People taking care of folks with asthma have a tough time figuring out the correct dose of corticosteroids," said editorial author Dr. Aaron Deykin, a pulmonologist at Brigham and Women's Hospital in Boston. He said people often minimize their symptoms.
"Because of the lack of a good tool for establishing the best dose of steroids, they're usually prescribed in a general range. For some this may be too low, but for many others it may be too much," said Deykin. "This paper shows that using [the exhaled nitric oxide] test, which is quite simple for the patient to perform, you can safely adjust the dose of steroid."
Taylor said the nitric oxide test is a simple breathing test, similar to the breathalyzer test used to measure the amount of alcohol in the blood. Currently, the machine is expensive -- around $30,000 -- but at least two companies are working on making portable, less costly machines that should be available within three years, according to Taylor.
The researchers assessed 46 people with asthma using the exhaled nitric oxide test and compared them to a group of 48 people whose asthma was assessed using conventional tools, such as symptom report, peak flow and pulmonary function testing.
All of the volunteers had been using inhaled corticosteroids. Using either the nitric oxide test or conventional measurements, the researchers adjusted the dose of the inhaled corticosteroids until the optimum dose for controlling asthma symptoms was achieved. Once the optimal dose was achieved, the volunteers were followed for 12 months.
The final average daily dose of fluticasone, the inhaled corticosteroid used in this study, was 370 micrograms for the nitric oxide group versus 641 micrograms for the conventional group -- a difference of more than 40 percent.
While the rates of asthma exacerbations were less than one per patient per year, according to the study, the nitric oxide group averaged 45 percent fewer exacerbations than the conventional group.
"In our lab in New Zealand, [nitric oxide measurements] are now used routinely and provide very important information to the clinician. They help us to get a clearer picture of the extent of airway inflammation in the bronchial tubes, and up till now that has not been possible," Taylor said.
Taylor cautioned there are two important limitations to using nitric oxide measurements. First, they may not be useful for all types of asthma, and second, the test is unreliable in people who are smokers.
Deykin also pointed out that the devices are still quite expensive, and can be difficult to maintain. Additionally, he said, people may not get reimbursed by their insurance companies for the test yet.
The study was released a day early to coincide with a presentation Tuesday at the American Thoracic Society international conference, in San Diego.
To learn more about asthma, visit the National Library of Medicine.