How A PFT Test Is Done?

Oct 05, 2022
How A PFT Test Is Done?
It is often found that if you have a wheezing noise coming from your mouth, your doctor immediately suggests you get a PFT. However, this is not just restricted to wheezing noises, but also some other crucial symptoms,...

It is often found that if you have a wheezing noise coming from your mouth, your doctor immediately suggests you get a PFT. However, this is not just restricted to wheezing noises, but also some other crucial symptoms, that make it essential for you to get the test done without any further due. 

If you are asked by your doctor to get a PFT test, then the first step is to get familiar with it.

What Is A Pulmonary Function Test? 

Before we discuss how a PFT test is done, we need to know what the term means. Pulmonary Function Tests, or PFTs, are a group of non-invasive tests that measure how well the lungs are functioning. They are used both as a diagnostic tool and to ascertain treatment response in patients suspected of or diagnosed with respiratory disease. 

Henceforth these tests provide valuable information regarding the airways, lung parenchyma, and the pulmonary capillary bed by taking into account gas flow and exchange rates and measuring lung capacity and volume. All this information is then used by healthcare providers to diagnose and subsequently treat underlying respiratory diseases. 

When Is A Pulmonary Function Test Recommended? 

If you report to the doctor with a history of the following, they will likely recommend a PFT test for further assessment and to confirm a diagnosis. 

  • Wheezing 
  • Coughing 
  • History of smoking 
  • Breathing difficulties 
  • Shortness of breath 
  • Fatigue 
  • Coughing up phlegm or mucus

How a PFT Test is done?

The way a pulmonary function test is performed depends on the patient and the disease/condition being tested for. Pulmonary test procedures are usually carried out in these ways, and you may be asked to perform one or more. How a PFT test is done on you depends on your doctor’s recommendation: 


A spirometer, also known as a breathing measurement device, is used to carry out one of the most common lung tests (spirometry). Spirometry measures airflow. The procedure is as follows: 

  • A diagnostician will instruct you to sit down while a soft clip is placed on your nose to ensure all breathing during the test is carried out by the mouth alone. 
  • You will be given a sterilized mouthpiece attached to a spirometer and asked to form a tight seal using your lips. 
  • You will then be asked to exhale and inhale into the apparatus forcefully. 
  • The procedure is usually repeated twice or thrice for accuracy 
  • Sometimes a bronchodilator is given to the patient, and spirometry is repeated to assess any improvements in the patient’s condition following medication administration. 

The test duration is approximately 30 minutes, a non-invasive test; hence, pain or discomfort is usually minimal to none. 

How A PFT Test Is Done? 1

Body Plethysmography 

It is a method used for lung volume measurement. It is the most accurate method to test lung capacity. The procedure is as follows: 

  • You will be asked to sit inside an enclosed transparent plastic box.
  • A nose clip is placed to ensure all breathing for the test is done through the mouth alone. 
  • You will be given a sterile mouthpiece and asked to form a tight seal around it using your lips. 
  • The mouthpiece attaches to an instrument used to measure breathing. 

As you breathe, a change of pressure inside the box is used for lung volume measurement. The test is non-invasive, thus causing minimum to no discomfort/ pain. The duration of the test is roughly 15 minutes.

Cardiopulmonary exercise test

How A PFT Test Is Done? 2

A CPET evaluates how your lungs, heart, and blood circulation perform during physical activities. 

  • This test is usually performed in a lab setting on a stationary bike or a treadmill. 
  • A diagnostician will then place EKG Monitors on your chest, blood pressure cuffs on your arm, a pulse oximeter on your finger, and a breathing measurement device with a mouthpiece to measure all your vitals during the test. 
  • You will then be asked to walk on the treadmill or pedal on the bicycle as the speed/resistance is gradually increased till you are fatigued and naturally come to a stop. 

This specialized test lasts for about 10-15 minutes 

How A PFT Test Is Done? 3

Diffusion Capacity Test

This test measures the amount of oxygen and carbon monoxide transported from your lungs to your bloodstream as you breathe. This method, too, uses a breathing measurement device with a mouthpiece. 

It quantifies the functioning of your air sacs (alveoli) responsible for the diffusion of these gasses to and from your bloodstream. 

How A PFT Test Is Done? 4

The test takes about 15 minutes to be carried out. 

Bronchial Provocation Test 

This test is usually carried out to diagnose or rule out asthma. It is used to assess the sensitivity of your lungs. 

You will be exposed to irritants that act as asthma triggers, e.g. smoke or methacholine, to see how your airway responds. 

How A PFT Test Is Done? 5

Occasionally exercise may also be used as a part of this test to gauge airway constriction.

Dr. Shahid Meer is expert in his field of pulmonology.

What Diseases/Conditions Can Be Diagnosed By A PFT? 

Moreover, while a PFT is most commonly used for diagnosis, it may also be used as routine screening for people exposed to work environments such as mining or graphite factories. In addition to that, they are also used to monitor treatment efficacy and progression of disease in individuals who have already been diagnosed with pulmonary disease. 

Doctors most commonly use a PFT to diagnose the following: 

  • Asthma 
  • Bronchitis 
  • Emphysema 
  • COPD 
  • Lung Cancer 
  • Asbestos 
  • Sarcoidosis 
  • Respiratory Infections 

If you use an inhaler and wonder Does Ventolin work immediately please read it.

What Does A PFT Measure? 

A pulmonary test procedure helps measure the following:

Tidal Volume (TV)

The volume of air inspired or expired during normal breathing 

Vital Capacity (VC) 

Amount of air exhaled after maximum inhalation 

Functional Residual Capacity (FRC) 

The volume of air that remains in the lungs after normal exhalation 

Residual Volume (RV)

The volume of air that remains in the lungs after forceful exhalation 

Total Lung Capacity 

The total amount of air in the lungs remaining after maximum inhalation 

Forced Expiratory Volume (FEV)

Amount of air exhaled during forced exhalation 

Peak Expiratory Flow Rate (PEFR)

The maximum speed of forced exhalation 

All of these quantifiable values are used to interpret and evaluate the functioning of your lungs. These values constitute the final PFT report handed to you/your doctor. 

How to Prepare For A PFT? 

When a patient’s pulmonary function test is advised, the doctor will usually ask for the patient’s medical history. Make sure to detail all your symptoms and any medications you use, including over-the-counter medications and supplements. 

Written consent is usually obtained from the patient before proceeding with the test. 

The doctor will also record your height and weight to calculate results accurately. 

Before the test, you may be advised to make certain habit changes a few hours in advance of the test, as detailed by your healthcare provider. These may include; smoking cessation, avoiding heavy meals and caffeine, and temporarily stopping certain medications that may interfere with the outcome of the test.

Please make sure to follow the advice of your healthcare provider and make sure to clarify any confusions or queries you might have. 

Risks Involved in a PFT

How a PFT test is done is usually a very low-risk procedure in itself, especially since this test is non-invasive. However, like any diagnostic procedure, there are some risks involved which include:

  • Shortness of breath 
  • Dizziness 
  • Onset of Asthma Attack 
  • Coughing 
  • Small risk of pneumothorax (collapsed lung) 

Contraindications of Pulmonary Function Test 

Listed below are situations under which a PFT is not recommended to be performed on the patient 

  • History of a collapsed lung (pneumothorax) 
  • Cardiac problems, e.g. chest pain, a recent history of heart failure 
  • Aneurysms in the abdomen, chest, or brain 
  • Respiratory infections 
  • Active Tuberculosis 
  • Recent eye surgery 

Factors That May Affect Your PFT Results 

The following factors may affect the accuracy of your PFT results: 

  • Pregnancy 
  • Use of bronchodilators
  • Patient cooperation and ability to follow instructions 
  • Use of pain-relieving medications 

How to Interpret Your PFT Results?

A PFT test is done on the recommendation of a medical professional; hence a referral is necessary to carry out a Pulmonary Test procedure. The results are usually available in the next 48 to 72 hours. 

  • Results are usually expressed as percentages and depend upon a person’s age, gender, ethnicity, and height. 
  • A value is considered abnormal if it is less than 80% of the predicted value. 
  • An abnormal test usually indicates the presence of a chest or lung disease. 

Your healthcare provider will discuss the findings of your report with you in detail and help you better understand your results. 


To summarize, a PFT test is done to measure lung capacity and assess how well your lungs are functioning. A PFT procedure is easier for the patient since it’s non-invasive and does not typically cause pain. However, it cannot be self-administered and requires the referral of a licensed medical professional.

Pulmonary function tests consequently are an important diagnostic tool recommended annually as routine screening to measure disease progress and treatment efficacy in people diagnosed with respiratory problems. 

Make sure to consult your healthcare provider or diagnostician if you have any further queries regarding how a PFT test is done.