The goals with initial testing are to diagnose asthma and evaluate its severity. Testing may be performed to distinguish asthma from other conditions that cause similar symptoms and to identify the presence of conditions, such as allergies, that have the potential to trigger or worsen asthma attacks. The goals with continued testing are to monitor lung function and asthma control, evaluate and resolve asthma attacks, and identify and address complications and side effects that arise.
The National Heart, Lung, and Blood Institute (NHLBI) National Asthma Education and Prevention Program (NAEPP) released "Expert Panel Report 3: Guidelines for the Diagnosis and Management of Asthma" in August 2007. These guidelines are intended to help guide the diagnosis and monitoring of those with asthma. They focus on assessing and monitoring asthma, educating people, encouraging them to participate in the management of their condition, controlling environmental factors that can trigger or exacerbate asthma attacks, and the use of medications.
Lung Function Tests and Imaging Studies
These are the primary tests used to diagnose, assess, and monitor asthma.
The NAEPP guidelines recommend:
- A detailed medical history and physical exam, focusing on the chest and respiratory tract
- Spirometry to evaluate narrowed or obstructed airways (FEV1; Forced Expiratory Volume in 1 second). This test measures the amount and rate of air exhalation as a person blows out through a tube. It can be performed on people 5 years of age or older to demonstrate airway obstruction that is reversible or partially reversible with a short-acting bronchodilator.
- "Challenge" tests that provoke the bronchi to constrict (Bronchial Provocation tests), such as exercise, cold air, methacholine, or histamine.
- Other pulmonary function studies and/or a chest x-ray
- Additional testing as required to help rule out other diagnoses or causes of the symptoms, such as cystic fibrosis, lung infections including tuberculosis, and gastrointestinal reflux
Asthma assessment and monitoring
- Spirometry – to evaluate lung function
- Peak expiratory flow (PEF) determination – measures the ability to push air out of the lungs or how fast air can be exhaled; this test uses a small device called a Peak Flow meter and can be performed by the person at home to monitor lung function.
- Pulse oximetry – a noninvasive way to continuously monitor O2 saturation; may be used in an emergency department or hospital to evaluate oxygen status.
- Chest x-ray
- Exhaled nitric oxide test test (FeNO; fraction of exhaled NO) – measures nitric oxide in exhaled breath; levels increase in the presence of inflammation of the airways, such as in those with asthma, and may rise and fall depending on the effectiveness of anti-inflammatory treatment. While this test may be useful in guiding the management of asthma patients, it is not yet recommended by NAEPP guidelines and so is not widely used.
For other lung function tests see, Johns Hopkins Medicine: Pulmonary Function Tests.
Laboratory testing is used to help rule out conditions that cause symptoms similar to asthma, to identify allergies, and to help identify and evaluate complications that arise. During severe asthma attacks, testing may be ordered to evaluate and monitor organ function, oxygen levels, and the body’s acid-base balance. Tests include:
- Blood testing for allergic sensitivity – blood tests that are specific for the allergen(s) suspected to be causing symptoms, such as dust mites, mold, pet dander, and pollens; may be ordered to help determine asthma triggers.
- Blood gases – an arterial blood sample is collected to evaluate blood pH, oxygen, and carbon dioxide; may be ordered when a person is having an asthma attack.
- CBC (complete blood count) – to evaluate blood cells and provide information on infection and inflammation
- CMP (comprehensive metabolic panel) – to evaluate organ function
- Theophylline – therapeutic drug monitoring if an individual with asthma is taking this medication
A healthcare practitioner will consider the results of the general tests, medical history, family history, and risk factors for certain diseases as well as the results of a physical examination. Based on these findings, some additional laboratory tests could be done. Other tests that may be occasionally ordered include:
- Tests to rule out cystic fibrosis, such as a sweat test or trypsin/chymotrypsin
- Sputum culture – to diagnose lung infections caused by bacteria
- AFB testing – to diagnose tuberculosis and nontuberculous mycobacteria (NTM)
- Lung biopsy – to evaluate lung tissue for damage and for cancer
- Sputum cytology – occasionally ordered to evaluate cells found in the lungs; eosinophils and neutrophils, two types of white blood cells, can be increased with inflammation in some people with asthma.
For additional laboratory testing that is sometimes performed, see Lung Diseases.