What are pulmonary function tests?

Pulmonary function tests (or lung function tests) include numerous procedures to diagnose lung problems. The two most common lung function tests used to diagnose asthma are spirometry, exhaled nitric oxide and challenge tests.

Spirometry — This is a simple breathing test that measures how much and how fast you can blow air out of your lungs. It is often used to determine the amount of airway obstruction you have. Spirometry can be done before and after you inhale a short-acting medication called a bronchodilator, such as albuterol. The bronchodilator causes your airways to expand, allowing for air to pass through freely. This test might also be done at future doctor visits to monitor your progress and help your doctor determine if and how to adjust your treatment plan.

Exhaled nitric oxide – Nitric oxide is a gas that is produced in the lungs and has been found to be an indicator of inflammation. Because asthma is an inflammatory process, this test has become helpful in the diagnosis and management of asthma. The test is performed by having you breathe into a small, handheld machine for about 10 seconds at a steady pace. It then calculates the amount of nitric oxide in the air you breathe out.

Challenge tests — These tests might be performed if your symptoms and screening spirometry do not clearly or convincingly establish a diagnosis of asthma. There are 2 types of challenge tests: methacholine and mannitol. These agents when inhaled, can cause the airways to spasm and narrow if asthma is present. During these tests, you will inhale increasing amounts of either methacholine aerosol mist or mannitol dry powder inhaler before and after lung function tests. The test is positive when your lung function drops during the challenge. A bronchodilator is always administered at the end of the test to reverse the effects of these agents.

How do I prepare for pulmonary function tests?

Ask your doctor if there is anything you need to do to prepare for spirometry.

Before taking a challenge test, be sure to tell your doctor if you have recently had a viral infection, like a cold, or any shots or immunizations, since these might affect the test's results.

Other general preparations to follow before the test include:

  • No smoking on the day of the test
  • No coffee, tea, cola, or chocolate on the day of test
  • Avoid exercise and cold air exposure on the day of test
  • Medicines taken to treat asthma can affect the test results. Different medicines must be stopped at different intervals. You will be told how long before testing to discontinue any medicines you are taking.

What is a chest X-ray?

An X-ray is an image of the body that is created by using low doses of radiation reflected on special film or a fluorescent screen. X-rays can be used to diagnose a wide range of conditions, from bronchitis to a broken bone. Your doctor might perform an X-ray exam on you in order to see the structures inside your chest, including the heart, lungs, and bones.

Last reviewed by a Cleveland Clinic medical professional on 06/10/2013.


  • Smith AD, Cowan JO, Filsell S, et al. Am J Respir Crit Care Med. 2004;169(4):473-478. Diagnosing Asthma Accessed 6/11/2013.
  • American Academy of Allergy Asthma & Immunology. Asthma Symptoms and Diagnosis Accessed 6/11/2013.
  • Kaminsky DA. Chapter 6. Asthma. In: Hanley ME, Welsh CH, eds. New York: McGraw-Hill; 2003. CURRENT Diagnosis & Treatment in Pulmonary Medicine Accessed 6/11/2013.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy