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Lung Function tests and imaging studies

These are the primary tests used to diagnose, assess, and monitor asthma.

Asthma diagnosis

  • There is no gold standard test for asthma and the diagnosis is based on a detailed medical history and physical examination, focusing on the chest and airways
  • Spirometry for patients 5 years old or older to demonstrate airway narrowing that can be overcome with an inhaler. This test measures the amount and rate of air exhaled as a patient blows out through a tube.
  • Additional testing as required to help rule out other diagnoses. This may include “challenges” that provoke the airways to constrict, such as exercise, cold air, methacholine or histamine, and a chest x-ray.

Asthma assessment and monitoring

  • 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.
  • Spirometry - to evaluate lung function
  • Pulse oximetry - measures oxygen in the blood by placing a small plastic device over the end of a finger. This may be used in hospital for an emergency to see if enough oxygen is getting around the body.
  • Chest x-ray - to look for signs of infections or other lung diseases such as a collapsed lung.

For other lung function tests see, Johns Hopkins Medicine: Pulmonary Function Tests.

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 of asthma. During severe asthma attacks, testing may be used to look for problems with oxygen levels, the body's acidity and signs of infection. Tests include:

  • Allergy testing (Immunoglobulin E total) – blood tests (e.g. IgE) that are specific for the allergen(s) suspected to be causing symptoms, such as dust mites, mould, pets and pollens.
  • FBC (Full blood count) – to look for signs of infection or the level of eosinophils (blood cells involved in a type of allergic reaction which may be raised in asthma)
  • Blood gases – an arterial blood sample is collected to look at acidity, oxygen, and carbon dioxide. Blood gases may be used in severe asthma attacks

Other tests that may be occasionally ordered, mainly to rule out other lung diseases:

For additional laboratory testing that is sometimes performed, see Lung Diseases.

Last Review Date: March 6, 2017