Lung Function Tests Explained: Spirometry, Preparation, and Results

Lung function tests, also called pulmonary function tests, measure how well air moves in and out of the lungs and how the lungs exchange gases. Spirometry is a common type: you breathe in deeply and blow into a mouthpiece, and the device measures how much air you exhale and how quickly. Other tests may measure lung volumes, gas transfer, or breathing during exercise. A clinician selects a test based on symptoms and the question being evaluated.

What the appointment may involve

For spirometry, a technician explains how to seal your lips around the mouthpiece and blow as strongly and fully as possible. You may repeat the maneuver several times to obtain consistent measurements. Some testing includes a medicine that opens the airways, followed by repeat measurements. Other pulmonary tests may involve breathing through a mouthpiece in a booth or walking on a treadmill while monitors record breathing and circulation.

Preparing for the test

Follow the instructions from your testing center. MedlinePlus notes that you may be asked to avoid a large meal, smoking, caffeine, alcohol, or heavy exercise for a particular period. If you use an inhaler, the clinic may give specific directions about whether and when to take it. Do not stop a prescribed inhaler or other medicine unless the clinician explicitly instructs you to. Tell the team about recent respiratory infections, pregnancy, surgery, or symptoms that make forceful breathing difficult.

How results are interpreted

Results are compared with expected values using factors such as age, height, and sex, and are considered alongside symptoms and medical history. An abnormal result can point toward an obstructive or restrictive pattern, but it does not always identify a specific disease. Additional testing may be needed. A normal result does not necessarily explain every symptom. Ask which measurement was abnormal, what it could indicate, and whether follow-up is recommended.

Safety and follow-up

Some people feel lightheaded, tired, or cough after forceful breathing. Tell the technician if you feel unwell. Sudden severe shortness of breath, blue lips, fainting, or severe chest pain requires urgent medical attention.

Sources and further reading

• Lung Function Tests — MedlinePlus Medical Tests, U.S. National Library of Medicine.

Health disclaimer

This article is for general education only. Its information and suggestions are not medical advice, diagnosis, or treatment and may not be right for everyone. Ask a qualified health professional for advice that fits your health, medications, and needs before changing your diet, exercise, supplement use, or care.