Tests
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 exacerbate 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.
Lung Function Tests and Imaging Studies
These are the primary tests used to diagnose, assess, and monitor asthma.
Asthma diagnosis
To diagnose asthma the NAEPP guidelines recommend:
A detailed medical history and physical exam, focusing on the chest and respiratory tract
Spirometry for patients 5 years old or older to demonstrate airway obstruction that is reversible or partially reversible with the inhalation of a short-acting bronchodilator. This test measures the amount and rate of air exhalation as a patient blows out through a tube. It is performed to evaluate narrowed or obstructed airways.
Additional testing as required to help rule out other diagnoses. This may include “challenges” that provoke the bronchi to constrict, such as exercise, cold air, methacholine, or histamine, other pulmonary function studies, and/or a chest x-ray.
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 patient 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 – The FDA has cleared a breath test that measures nitric oxide in exhaled breath. Nitric oxide is a substance normally present in very small quantities in the breath, but levels increase in the presence of inflammation of the airways such as in patients with asthma. Levels 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, John Hopkins Medicine: Pulmonary Function Laboratory.
Laboratory Tests
Laboratory testing is used to help rule out conditions that cause symptoms similar to asthma, to identify patient 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:
Allergy testing – 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 patient is having an asthma attack.
CBC (Complete Blood Count) – to evaluate blood cells
CMP (Comprehensive Metabolic Panel) – to evaluate organ function
Theophylline – therapeutic drug monitoring if patient is taking medication
Other tests that may be occasionally ordered:
Cystic fibrosis tests – to rule out cystic fibrosis
Sputum culture – to diagnose lung infections caused by bacteria
AFB smear and culture – 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 asthma patients.
For additional laboratory testing that is sometimes performed, see Lung Diseases.
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