The bronchial challenge test assesses airway sensitivity. It helps healthcare professionals determine if your airways are hyperresponsive, meaning they react more strongly than usual to certain stimuli. This test measures how much your airways narrow in response to specific agents.
Reasons for the Test
A bronchial challenge test is often used when asthma or other reactive airway conditions are suspected, but routine lung function tests like spirometry are inconclusive. It is useful for individuals with symptoms such as chronic cough, wheezing, chest tightness, or shortness of breath, especially if these are intermittent or triggered by exercise or cold air. The test helps link these symptoms to airway hyperresponsiveness, even if baseline lung function appears normal.
How the Test is Performed
Before the test, you will receive specific instructions. These often include stopping certain medications, such as inhalers and antihistamines, for hours to several days. Avoiding caffeine, alcohol, and strenuous exercise for several hours prior to the test is advised. Informing the healthcare provider about any recent respiratory infections is crucial, as these can temporarily increase airway responsiveness.
The test begins with a baseline spirometry measurement to assess your initial lung function. Spirometry involves breathing into a device that measures how much air you can exhale and how quickly. After this baseline, you will inhale a challenging agent through a nebulizer or a handheld device.
The most common agent used is methacholine, which causes mild airway narrowing by stimulating smooth muscle receptors in the airways. Other agents like mannitol (a powdered sugar) or an exercise challenge may also be used, depending on the suspected triggers. With methacholine or mannitol, increasing doses are administered in a stepwise manner, with spirometry performed after each dose to monitor changes in lung function. For an exercise challenge, you might walk on a treadmill or ride a stationary bike at increasing intensity, followed by spirometry measurements. The test continues until a significant drop in lung function occurs or a maximum dose of the agent is reached.
Interpreting Your Results
Interpreting bronchial challenge test results focuses on changes in your lung function, specifically the forced expiratory volume in one second (FEV1). A significant decrease in FEV1 indicates airway hyperresponsiveness. A positive test shows a 20% or greater reduction in FEV1 from your baseline measurement. This reduction is often referred to as the “provocation dose” (PD20) or “provocation concentration” (PC20), which indicates the amount of challenging agent needed to cause the FEV1 to drop by 20%.
A positive result suggests sensitive airways that react easily to stimuli, supporting a diagnosis of asthma or other reactive airway conditions. Conversely, a negative result, with no significant FEV1 drop even at the highest dose, helps rule out asthma. While a positive test points towards airway hyperresponsiveness, other conditions can also cause this, so results are considered alongside your medical history.
What to Expect During the Test
During the bronchial challenge test, healthcare professionals will monitor you. You might experience mild symptoms like a cough, slight shortness of breath, or chest tightness as your airways react to the challenging agent. These sensations are expected and indicate how your airways respond to irritation.
The medical team is prepared to manage any significant reactions. If your breathing becomes too difficult or your lung function drops considerably, the test will be stopped immediately. A bronchodilator medication, which helps open the airways, will be given to quickly reverse any induced bronchospasm and alleviate symptoms. After the test, your lung function will be re-checked to ensure it has returned to normal before you leave.