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What are PFTs?

by | Mar 30, 2023 | Sleep Studies

Pulmonary function tests (PFTs) are diagnostic tests used to determine how well your lungs work. These non-invasive tests measure how much air the lungs can hold, how quickly air moves in and out of the lungs, and how efficiently the lungs transfer oxygen into the bloodstream. PFTs commonly diagnose lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis.

Types of PFTs

There are several types of PFTs, including spirometry, lung volume tests, and diffusion capacity tests.


Spirometry is the most commonly used test which measures how much air you can inhale and exhale. It also estimates how much air is in your lungs. During a PFT, a patient typically sits in a machine called a spirometer. The patient takes a deep breath and exhales forcefully into the mouthpiece of the spirometer. The spirometer measures the amount of air exhaled and how quickly it was exhaled. The test is usually repeated several times to ensure accuracy.

Lung Volume Tests

Lung volumes, or body plethysmography, measure the various amounts of air in your lungs after different points of inhalation and exhalation. Lung volume tests use a technique called plethysmography. The patient sits in a small, airtight chamber and breathes in and out of a mouthpiece. The equipment measures pressure and volume changes in the chamber, along with the amount of air in the lungs.

Diffusion Capacity Tests

Diffusion capacity tests assess how effectively the lungs transfer oxygen from the air to the bloodstream. The patient inhales a small amount of gas, usually carbon monoxide or helium, which is then measured in the bloodstream. The test is painless and non-invasive.

Why Might I Need a PFT?

There are many different reasons for using pulmonary function tests (PFTs). They can be part of a routine physical or to ensure employee health. PFTs can be used to evaluate patients before surgery or other medical procedures to ensure their lungs function properly. Your healthcare provider may utilize PFTs if they need help diagnosing a health problem such as:

  • Allergies
  • Respiratory infections
  • Trouble breathing from injury to the chest or a recent surgery
  • Chronic lung conditions
  • Asbestosis
  • Restrictive airway problems
  • Sarcoidosis
  • Scleroderma

Important But Not Foolproof

PFTs are important tools for diagnosing lung diseases and assessing lung function. They are used to detect lung diseases in their early stages, monitor the progression of lung diseases, and determine the effectiveness of treatments. However, it is necessary to note that PFTs are not foolproof and can sometimes produce inaccurate results. Varying factors can affect the accuracy of the test results, including:

  • Poor patient effort
  • Poor equipment calibration
  • Certain medications

Additionally, PFTs can not diagnose all lung diseases and may need to be supplemented with other diagnostic tests, such as chest X-rays or CT scans.

PFTs are a valuable tool for assessing lung function and diagnosing lung diseases. They are non-invasive, relatively simple to perform, and provide important information about how the respiratory system is functioning. PFTs are most beneficial when used with other diagnostic tests to ensure accurate diagnoses and effective treatments. A professional clinic can run PFTs and prioritize individual health. The Comprehensive Sleep and Breathing Disorders Center evaluates each patient individually and conducts a thorough analysis of underlying problems.