Pulmonary Function Testing: A Comprehensive Guide to Understanding and Interpreting Results

Pulmonary Function Tests are essential tools in the diagnosis and management of respiratory diseases. They help in identifying the cause of respiratory symptoms, assessing the severity of pulmonary disorders, and guiding the treatment process. Here’s what you need to know about these critical diagnostic tests.

What is Pulmonary Function Testing?

PFT encompasses a series of non-invasive tests that measure how well the lungs take in and release air and how efficiently they exchange gases. These tests are performed using a device known as a spirometer, along with other equipment designed to assess lung function comprehensively.

Types of Pulmonary Function Tests


The most common PFT, spirometry, measures the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. It’s pivotal for diagnosing conditions like asthma and COPD.

Lung Volume Testing

These tests measure the volume of air in the lungs, including the total lung capacity (TLC), the amount remaining after a normal exhale (functional residual capacity, or FRC), and the volume left after a forced exhale (residual volume, RV).

Gas Exchange Testing

This involves tests like the diffusion capacity to measure how well oxygen and other gases are being absorbed into the blood from the lungs.

Body Plethysmography

This test measures the total amount of air your lungs can hold. It’s useful for diagnosing conditions that cause abnormalities in lung volume.

Exercise Stress Tests

These assess the lungs’ performance during physical activity and can help determine the cause of shortness of breath.

Preparing for Pulmonary Function Testing

Preparation for PFT may vary depending on the specific tests you’re scheduled to undergo. Generally, you may be advised to avoid using inhaled bronchodilators or inhalers for a certain period before the test. Wearing loose clothing and avoiding heavy meals before the test can also help ensure more accurate results.

Interpreting PFT Results

Interpreting PFT results can be complex and should always be done by a healthcare professional. Here are some key terms and values often discussed in PFT results:

  • FVC (Forced Vital Capacity): The maximum amount of air you can forcefully exhale after a deep breath.
  • FEV1 (Forced Expiratory Volume in One Second): The amount of air you can force out in the first second of an FVC test.
  • FEV1/FVC Ratio: Used to diagnose obstructive and restrictive lung diseases. A lower than normal ratio suggests obstructive lung disease, while a normal or high ratio might indicate restrictive lung disease.
  • TLC (Total Lung Capacity): The total volume of air in the lungs after taking the deepest breath possible.
  • DLCO (Diffusion Capacity): Measures how well gases are transferred from the lungs to the bloodstream.

Normal vs. Abnormal Results

  • Normal Results: Indicate that the amount and speed of air that can be inhaled and exhaled from your lungs are within the typical range for your age, sex, race, and height.
  • Abnormal Results: May suggest the presence of respiratory conditions. Lower than normal values can indicate obstructive lung diseases like COPD or asthma, while higher values may point to restrictive lung diseases such as pulmonary fibrosis.

Pulmonary Function Testing is a vital component in diagnosing and managing respiratory conditions. While the tests provide critical data about lung function, interpreting these results requires professional expertise. If you undergo PFT, ensure to discuss the results in detail with your healthcare provider to understand what they mean for your respiratory health and treatment plan.

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