Nitric oxide (NO) is a gas released by cells in the lungs. When a person with allergies and/or asthma experiences an inflamed airway, the inflammatory cells release more NO and the NO levels increase. Due to this fact, fractional concentration of exhaled NO (FeNO) is an increasingly used tool in the diagnosis and management of asthma in children and adults. However, new research found that what was once defined as the "normal" range of FeNO concentrations in children may not hold true for all children.
The range of FeNO levels considered to be normal appear to be different for Caucasian, Asian-Canadian, and African-Canadian children. Researchers caution that by not taking factors, such as race, into consideration, disease mismanagement or a wrong diagnosis may occur.
"Doctors often assume that high FeNO levels mean that a child has asthma or, in a child who is already diagnosed with asthma, that the disease isn't very well controlled. It's important for them to realize that factors other than asthma can affect FeNO values," said lead researcher Tom Kovesi, MD, pediatric respirologist at the Children's Hospital of Eastern Ontario and associate professor of pediatrics at the University of Ottawa, ON, Canada. "Using our data, we defined the normal range of FeNO concentrations in healthy children of different racial ancestry and looked at factors that affected that range."
Dr. Kovesi and his colleagues from Health Canada used data obtained during a large study on children's lung health in Windsor, ON, Canada, to help them determine the normal range of FeNO concentrations in 657 healthy children between the ages of 9 and 12. The average FeNO level for each child was measured using a machine that determined the amount of NO by an exhaled breath into a mouthpiece. Once the FeNO levels were determined, researchers compared them to the children's other characteristics, including race, age, and height.
"We looked at other factors that we thought could potentially alter FeNO levels, and we found that FeNO levels were a lot higher in the Asian-Canadian children when compared with the Caucasian children," Dr. Kovesi said. "We also found an increase in FeNO levels in the children that were older and who were taller."
Results showed that while the Caucasian children had an average FeNO level of 13 parts per billion (ppb), the average level for Asian-Canadian children was nearly double, at 24 ppb. The average level for African-Canadian children was 18 ppb. This means that, in healthy children of African or Asian ancestry, FeNO levels are higher than the concentrations usually felt to be normal by physicians. Dr. Kovesi was surprised by the large difference in FeNO levels in children of different racial origins, and noted that more research on genetic differences is needed to better explain why. In the meantime, parents should be aware that what is considered a normal FeNO level for their child could be different from that of their child's classmate.
"Controlling airway inflammation is essential for improving asthma control and outcomes," Dr. Kovesi said. "FeNO is still one of the most important tools physicians have to determine when airway inflammation has worsened, so treatments can be modified to improve control. Families should be aware that there are other factors that can affect their children's FeNO measurement, particularly if they are of African or Asian ancestry."
"While there have been many advancements in the proper diagnosis and management of airway disorders such as asthma, it is crucial that physicians continue to use new research (as provided in this study) to help ensure that children and adults receive appropriate testing and care," said Alvin V. Thomas, Jr., MD, FCCP, President of the ACCP.
This research was published in the January issue of the journal Chest.
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