Spirometry is the only objective method to diagnose Obstructive Airways Diseases (Asthma and COPD). It also help  in monitoring  the treatment .Most of the doctors diagnose Asthma only by obtaining history and listening lung sounds with a stethoscope. However  with this approach 65% of patients suffering from obstructive airway disease remain undetected . More than 75% of asthma and COPD sufferers in India have never undergone spirometry testing.

This test determines how much air your lungs can hold, how quickly you can move air in and out of your lungs.Asthma_Test

The tests can diagnose lung diseases, measure the severity of lung problems, and check to see how well treatment for a lung disease is working.

Lung function tests are done to:

  • spirometry help to Determine the cause of breathing problems for example it can differentiate between breathlessness due to a cardiac cause and breathlessness due to a respiratory cause.

  • Diagnose certain lung diseases, such as asthma or chronic obstructive. pulmonary disease (COPD).

  • Evaluate a person’s lung function before surgery.

  • Occupational asthma is common in peoples exposed to toxic substances at workplace for example peoples working  in oil paint industry, soldering,welding, animal products, chemicals, steel factories and others, which are known risk factors for asthma or COPD, should be routinely screened before the start of their jobs to look for presence of underlying OAD. accounts for about 10-20% of all asthma cases.

  • Encouragement and motivation for smoking cessation,

  • Check the effectiveness of treatment for asthma and other lung diseases.

The testing may take from 5 to 30 minutes, depending upon how many tests are done.

How the Test is performed?

welding, animal products, chemicals, steel factories and others, which are known risk factors for asthma or COPD, should be routinely screened before the start of their jobs to look for presence of underlying OAD. 

Spirometry measures airflow. By measuring how much air you exhale, and how quickly, spirometry can evaluate a broad range of lung diseases. In a spirometry test, while you are sitting, you breathe into a mouthpiece that is connected to an instrument called a spirometer. The spirometer records the amount and the rate of air that you breathe in and out over a period of time.

How to Prepare for the Test?

Do not eat a heavy meal before the test

Do not smoke for 4 – 6 hours before the test

you need to stop using bronchodilators or inhaler medications

You may have to breathe in medication before or during the test.

How the Test Will Feel?

Since the test involves some forced breathing and rapid breathing, you may have some temporary shortness of breath or lightheadedness. You breathe through a tight-fitting mouthpiece, and you’ll have nose clips.

Why the Test is performed?

Pulmonary function tests are done to:

  • Diagnose certain types of lung disease (such as asthma, bronchitis, and emphysema)

  • Find the cause of shortness of breath

  • Measure whether exposure to chemicals at work affects lung function

  • Check lung function before someone has surgery

It also can be done to:

  • Assess the effect of medication

  • Measure progress in disease treatment

Normal Results

Normal values are based upon your age, height, ethnicity, and sex. Normal results are expressed as a percentage. A value is usually considered abnormal if it is less than 80% of your predicted value.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

Different measurements that may be found on your report after spirometry include:

  • Expiratory reserve volume (ERV)

  • Forced vital capacity (FVC)

  • Forced expiratory volume (FEV)

  • Forced expiratory flow 25% to 75%

  • Functional residual capacity (FRC)

  • Maximum voluntary ventilation (MVV)

  • Residual volume (RV)

  • Peak expiratory flow (PEF).

  • Slow vital capacity (SVC)

  • Total lung capacity (TLC)

What Abnormal Results Mean?

Abnormal results usually mean that you may have some chest or lung disease.

Some lung diseases (such as emphysema, asthma, chronic bronchitis, and infections) can make the lungs contain too much air and take longer to empty. These lung diseases are called obstructive lung disorders.

Other lung diseases make the lungs scarred and smaller so that they contain too little air and are poor at transferring oxygen into the blood. Examples of these types of illnesses include:

  • Extreme overweight

  • Fibrosis of the lungs

  • Lung cancer

  • Sarcoidosis and scleroderma


The risk is minimal for most people. There is a small risk of collapsed lung in people with a certain type of lung disease. The test should not be given to a person who has experienced a recent heart attack, or who has certain other types of heart disease.


Your cooperation while performing the test is crucial in order to get accurate results. A poor seal around the mouthpiece of the spirometer can give poor results that can’t be interpreted. Do not smoke before the test.

Absolute contraindication

  • Cardiac surgery/Myocardial Infarction in the past 1 month

  • Recent thoracic/abdominal/eye surgery in the past 1 month

  • History of pulmonary embolism

  • History of aneurysms abdominal/tho­racic/ cerebral

  • Presence of facial palsy/contractures

  • Patient unwilling to perform the test.

Activities that should be avoided before Pulmonary function testing 

  • Smoking tobacco in any form in the last 2-4 hrs

  • Consuming tea/coffee/caffeinated drinks in the past 6 hr

  • Heavy meal in past 4 to 5 hour

  • Heavy exercise in the past ½ hour

  • Bronchodilators: inhaled/oral

  • Alcohol

  • Lower respiratory tract infection in the past 15 days

  Medication Wash out Restrictions:

Short acting Beta2 Agonists (Eg. Salbutamol, Levosalbutamol)Long Acting Beta2 Agonists (Eg. Formoterol, Salmeterol)Long acting Antimuscarinic bronchodilators Tiotropium

Long acting Theophyllines

Short Acting Antimuscarinic bronchodilators .e.g. Ipratropium

Inhaled steroids

6 hrs12 hrs24 hrs

24-48 hrs

8 hrs

1 hr

If above mentioned restrictions are not observed, then the spirometry readings may not be accurate and show false high levels. Moreover, bronchodilator reversibility will be unreliable.

Role of PFT in smoking cessation

Various scientific  Studies conducted in western countries have found that Spirometry can double the chance of smoking cessation by using the concept of lung age. 

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