Asthma Diagnosis: Evaluating Adults and Infants Through Appropriate Testing
Asthma, a common respiratory condition that affects millions worldwide, is often diagnosed through a series of tests designed to assess lung function and identify potential triggers. This article will explore the key diagnostic tests used to diagnose asthma in adults.
Lung Function Testing
Lung function testing is the primary method used to diagnose asthma in adults. These tests assess airflow limitation and reversibility, which are crucial indicators of asthma.
Spirometry
Spirometry is a common lung function test that measures how much air a person can exhale and how quickly this happens after taking a deep breath. The patient blows into a device called a spirometer, providing values such as Forced Expiratory Volume in 1 second (FEV1). Reversibility testing is done by repeating spirometry after inhaling a bronchodilator (medication that opens airways). Improvement of FEV1 by more than 12% and at least 200 ml supports asthma diagnosis [1][2][5].
Methacholine Challenge Test
The methacholine challenge test involves inhaling methacholine, a substance that causes airway narrowing in susceptible people. Spirometry is performed afterward to detect airway hyper-responsiveness, which can indicate asthma in cases where baseline spirometry is normal [1][4].
Exercise Challenge Test
The exercise challenge test reproduces asthma symptoms by increasing ventilation. Lung function is measured before and after exercise using spirometry, diagnosing exercise-induced asthma by detecting a decrease in lung function triggered by physical activity [1].
Peak Flow Monitoring
Peak flow monitoring is a test used by those with asthma to manage their condition, not diagnose it. Patients measure peak expiratory flow at home over days or weeks to detect variability in airway obstruction [3].
Allergy Testing
Allergy testing can help identify allergic triggers contributing to asthma. Skin prick tests or blood tests (such as RAST) can identify allergens causing inflammation, guiding management by avoidance or treatment of allergic triggers [4].
Other Investigations
Chest X-rays or CT scans may be done to exclude other conditions mimicking asthma symptoms [2].
How These Tests Work
- Spirometry quantifies airflow limitation and its responsiveness to bronchodilators to distinguish asthma (reversible obstruction) from other lung diseases like chronic obstructive pulmonary disease (COPD) [1][5].
- The methacholine challenge provokes airway narrowing in hyperresponsive airways, revealing asthma in cases where baseline spirometry is normal [1][4].
- The exercise challenge reproduces symptoms by increasing ventilation, detecting exercise-induced bronchoconstriction [1].
- Allergy tests identify specific allergens causing inflammation, guiding management by avoidance or treatment of allergic triggers [4].
These tests, combined with clinical history and symptom patterns, form the basis for diagnosing asthma in adults. No single test confirms asthma alone; diagnosis usually requires integration of clinical and functional findings over time [5].
A doctor will review a person's medical history, asking about symptoms, triggers, family history, smoking habits, and work environment. A history of allergies or eczema increases the risk of developing asthma. Asthma affects 7.8% of people in the United States, with 8.4% of adults and 5.8% of children having the condition in 2020. Frequent follow-up visits may be necessary to manage asthma symptoms effectively.
Upon diagnosis, a person with asthma will receive an individualized treatment plan from a doctor, including which asthma medications to use. Further tests, such as allergy testing, blood testing for eosinophils and immunoglobulin E, imaging tests like X-rays, and gas transfer tests, can be recommended after an asthma diagnosis to guide treatment or provide more details.
The FeNo test measures the amount of nitric oxide in a person's breath as a marker of lung inflammation. High levels of nitric oxide during a FeNo test could indicate inflamed airways.
In summary, the diagnosis of asthma in adults primarily involves lung function testing to assess airflow limitation and reversibility, as well as tests to identify triggers or rule out other conditions. No single test confirms asthma alone; diagnosis usually requires integration of clinical and functional findings over time.
- Lung function testing, particularly spirometry, is the primary method used to diagnose asthma in adults, as it assesses airflow limitation and reversibility.
- Reversibility testing during spirometry is done by inhaling a bronchodilator to open airways, with improvement of FEV1 by more than 12% and at least 200 ml supporting asthma diagnosis.
- The methacholine challenge test involves inhaling methacholine to cause airway narrowing and detect airway hyper-responsiveness, indicating asthma in cases where baseline spirometry is normal.
- The exercise challenge test reproduces asthma symptoms by increasing ventilation, detecting exercise-induced asthma by finding a decrease in lung function triggered by physical activity.
- Chemistry scans like the FeNo test measure nitric oxide in a person's breath as a marker of lung inflammation, with high levels indicating inflamed airways.
- Allergy testing, such as skin prick tests or blood tests, can help identify allergic triggers that contribute to asthma, guiding management through avoidance or treatment of allergic triggers.
- Seekers with asthma may pursue other investigations, such as chest X-rays or CT scans, to rule out other conditions mimicking asthma symptoms, or undergo further tests like allergy testing or blood testing to guide treatment or provide more details.
