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Wednesday, April 20, 2011

Diagnosing Asthma in Children: What is the role of Bronchoprovocation testing?

Asthma is more common in boys than in girls during childhood.  After puberty, asthma is more common in girls. Many children who have wheezing in the preschool years do not go on to have asthma by school age. Because asthma can be so different from child to child in this age group, diagnosing asthma can be difficult.  This leads to both over diagnosis AND under diagnosis of asthma.

Asthma usually starts before the age of 6 and can be divided into 3 categories:
Transient (temporary) early wheezers,  non-allergic wheezers, and true persistent asthma.  In the 6-11 year age group, the number of children with asthma but no allergies decreases and the number of children with asthma AND allergies increases.

Airway hyperresponsiveness (AHR) is an important symptom of asthma.  AHR means the airways are extra sensitive and tighten when stimulated.  Airways can be stimulated using exercise or chemicals that are inhaled such as histamine or methacholine. Stimulating airways in this manner to see how sensitive they are is called “bronchoprovocation testing”. 

Bronchoprovocation testing using “methacholine”is safe and often used to help confirm or diagnose asthma in school age children. In this test, patients inhale increasing amounts of methacholine. A breathing test is done before every increase to see if their airways have reacted by tightening.  This test is called a "Methacholine challenge" (MCH).

Our research questions:
  • Does measuring Airway Hyper-responsiveness through MCH help physicians diagnose asthma? 
  • How accurate are the results?  Do most children with asthma have a positive MCH?  Do most children without asthma have a negative MCH?
  • Does gender or allergic status influence the results of MCH testing?

  • 228 children with asthma participated – 151 children had allergic asthma, 77 non-allergic asthma.
  • 197 “healthy” children participates. (no asthma, no allergies, no rhinitis (hayfever))
All children performed a MCH test then the results were analyzed.

Using MCH to diagnose asthma in non-allergic school age children (especially boys) is not useful.  In this group of non-allergic children, every time a test is “positive”, there is a 50-50 chance that it is actually a true positive.  Half the time, when the test is “positive”, the child does not actually have asthma.

MCH testing was more useful to confirm a diagnosis of asthma in school age children who have allergies.

Conclusion: Asthma often changes in the school age child with allergies playing a bigger role in the kids with persistent asthma. The best way to diagnoses asthma in this age group is through a detailed history of symptoms, including the presence of allergies.

When interpreting the results of a MCH, it is very important to take note of a child’s gender and the presence of allergies.  In a male child without allergies, the results of a MCH test alone cannot be used to diagnose asthma.

Diagnosing asthma in children: what is the role for methacholine bronchoprovocation testing?  Liem JJ, Kozyrskyj AL, Cockroft DW, Becker AB. Pediatr Pulmonol. 2008 May;43(5):481-9