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Difference Between Spirometry for Asthma and Spirometry COPD

Spirometry for asthma is when this lung function test is used to test for airflow obstruction that could indicate asthma. Spirometry for COPD is when spirometry is used to test for chronic obstructive pulmonary disease.

What is Spirometry for asthma?


Spirometry for asthma is a test to measure breathing ability to help diagnose if a person has asthma.


The way spirometry works is a patient is told to breathe in and out in such a way that breathing ability and lung capacity can be calculated and compared against standard reference values. Values that deviate from the reference values can help indicate if a patient has asthma or some other obstructive breathing condition. The FEV1 is how much air is forcibly breathed out. This is often measured along with the FVC. The FEV1 is termed forced expiratory volume measured per second and FVC is forced vital capacity, this is how much air is forcibly breathed in.

Diagnostic values:

The FEV1 increases by 12% after use of a bronchodilator. Spirometry readings stabilize in cases of chronic asthma. The ratio of FEV1/FVC is often normal in asthmatics but may decrease about 5% from normal in very sick patients.


Spirometry is a useful measure of lung function and can help in diagnosis of asthma in patients, and it can show if medicine is being effective in treating the problem.


Not every asthmatic has abnormal spirometry results. Asthma triggered by allergens may not show abnormal FEV1 or FVC, requiring additional tests for diagnosis to be made. 

What is Spirometry COPD?


Spirometry for COPD (chronic obstructive pulmonary disease) is a breathing test that can be used to measure airflow and assist in the diagnosis of COPD.


The method of spirometry for COPD is done in the same way as for asthma. The forced inspiration and forced expiration of air are measured over a set unit of time, and then these values are compared with normal values.

Diagnostic values:

The FEV1/FVC are less than 70% or below the lower limit of what is considered a normal value. After use of a bronchodilator the spirometry values do not improve. Spirometry readings do not stabilize over time with COPD, because it worsens in time. The ratio of FEV1/FVC is always reduced from normal even in cases of mild COPD, so this is one way that it differs from asthma.


Spirometry can be useful for indicating COPD in patients especially when combined with a clinical exam and if a person is older than 40 and has lifestyle factors, such as smoking, which makes them more likely to have obstructive lung diseases.


While spirometry is a good measure for helping doctors detect COPD, it is a test that cannot always be performed in patients with certain conditions such as TB or someone who is actively coughing up blood.

Difference between Spirometry for asthma and Spirometry COPD


Spirometry for asthma is when spirometry is done to test if a person has asthma. Spirometry for COPD is when spirometry is done to test if a person has COPD.


The ratio is less than 70% in the case of an attack of asthma. The ratio is less than 70% in the case of COPD and this becomes worse in time.


The FVC is sometimes reduced in the case of asthma. The FVC is always reduced in the case of COPD.


The FEV1 increases after bronchodilator treatment if a person has asthma. The FEV1 does not improve after bronchodilator treatment if a person has COPD.

Normal/abnormal spirometry readings

Sometimes abnormal with asthma but may be normal in patients with allergen-induced asthma. Always abnormal values with COPD since it is a progressive disease.

Serial spirometry

Results of spirometry can vary from time to time with asthma. Results of spirometry with COPD become worse in time.

Table comparing Spirometry for asthma and Spirometry for COPD

Summary of Spirometry for asthma and Spirometry for COPD

  • Spirometry is done to help diagnose asthma and COPD.
  • Asthma values may vary with spirometry and do improve with treatment.
  • COPD is progressive so spirometry readings do not improve and only worsen with time.


How is COPD diagnosed with spirometry?

COPD is diagnosed by recording measures of the amount of air inhaled versus exhaled in a given amount of time. It is specific ratios of forced expiration and inspiration values that indicate COPD; these don’t improve with bronchodilator treatments.

What spirometry indicates asthma?

A lower-than-normal ratio of FEV1 to FVC and  decreased FEV1 indicate asthma. The FEV1 also rises after treatment, a further good sign that the person has asthma.

Is it possible to have asthma and COPD together?

Yes, it is possible to have both COPD and asthma at the same time. This is called asthma-COPD overlap syndrome (ACOS). People with ACOS have symptoms much more often than people with only one of the two conditions. They also tend to produce more mucus and have a harder time breathing. As a result, patients with ACOS usually need treatment more frequently and may visit the hospital more often than patients who only have COPD or asthma.

What is abnormal spirometry?

Abnormal spirometry is when the values recorded of the patient’s breathing are not in the normal range. The FEV1 and FVC are specifically relevant in terms of how much below normal they are and what the ratio of the two is. Specific values can be used to diagnose asthma or COPD or a range of other problems related to pulmonary function.

What is a good score on a spirometry test?

A person who has no obstructive breathing problem would have good spirometry scores as follows: FEV1 more than 80%, FVC more than 80%, and the ratio of FEV1 to FVC would be more than 70%.

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References :

[0]Barreiro, Timothy, and Irene Perillo. "An approach to interpreting spirometry." American family physician 69.5 (2004): 1107-1114.

[1]Ponce, Mario C., and Sandeep Sharma. "Pulmonary function tests." StatPearls [Internet]. StatPearls Publishing, 2020.

[2]Yawn, Barbara P. "Differential assessment and management of asthma vs chronic obstructive pulmonary disease." The Medscape Journal of Medicine 11.1 (2009): 20.

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