Chronic obstructive pulmonary disease (COPD) is a condition that obstructs airflow. A spirometry test shows how a person’s lungs are functioning and can help diagnose and grade the severity of COPD.

Spirometry is a valuable tool in the diagnosis of several conditions that affect breathing.

It measures the amount of air a person can exhale after a deep inhalation. It is not painful and often takes under 10 minutes. After the test, a person may feel lightheaded or tired.

Keep reading to learn about spirometry and the diagnosis of COPD. This article also looks at how doctors may use it to track disease progression and determine treatment.

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Spirometry is the standard breathing test for the diagnosis of COPD.

Doctors use it to:

  • detect COPD in people with exposure to risk factors, mainly tobacco smoke, whether they have symptoms or not
  • confirm an airway obstruction
  • determine the severity of airflow obstruction in COPD
  • help establish treatment goals
  • monitor response to therapy
  • help predict outcomes and long-term survival

In a spirometry test, a person blows air into a mouthpiece with tubing. The tubing attaches to a small, computerized machine.

The technician who administers the test instructs the person to inhale deeply and fully and then exhale hard and fast. They repeat this multiple times. Afterward, the person may feel tired or lightheaded.

The machine shows the amount of air the person blows out, as well as the speed with which they blow it. These measurements reveal accurate information about their lung function.

Spirometer measurements

A full inhalation followed by a forced exhalation allows the spirometer to take the following measurements:

  • Forced vital capacity (FVC): This is the volume of air that a person can forcibly exhale in one breath. It is a different measurement from vital capacity, which is the maximum air that someone can exhale after a full inhalation, whether they forcibly exhale or not.
  • Forced expiratory volume in 1 second (FEV1): This is the volume of air an individual can exhale in the first second of a forced exhalation.
  • Ratio of FEV1 to FVC (FEV1/FVC): This ratio, along with FVC and FEV1, are the key measurements that doctors use to make a diagnosis of COPD.

To diagnose COPD, a doctor considers a person’s symptoms, medical history, and the results of their spirometry and other tests.

Some symptoms of COPD include:

The medical history involves the doctor asking questions about:

  • smoking or exposure to secondhand smoke
  • exposure to chemicals or air pollution
  • whether or not family members have had COPD

Besides spirometry, some other diagnostic tests include chest X-rays, which produce an image of the lungs and other structures in the chest, and arterial blood gas, which is a measurement of oxygen in the blood.

The new guidelines for staging COPD take into account two factors: airflow obstruction and symptom history. Doctors can assess airflow obstruction using a spirometer to measure FEV1.

The staging system provides a number to demonstrate the severity of the airflow obstruction:

GOLD 1above 80
GOLD 250–70
GOLD 330–49
GOLD 4below 30

Doctors also assess a person’s symptom history and assign them a letter using either the Modified Medical Research Council (mMRC) questionnaire or the COPD assessment test (CAT):

Moderate or severe exacerbation history
2 (or above) or 1, leading to hospital admissionCD
0 or 1, not leading to hospital admissionAB
mMRC 0–1
CAT below 10
mMRC above 2
CAT above 10

For example, if someone with an FEV1 of below 30 has a CAT score of below 10 and has experienced one or more moderate exacerbations, a doctor would describe their stage as GOLD 4 group C.

Learn more about COPD stages and their symptoms here.

One 2014 research article notes that the presence or absence of symptoms is not a reliable indicator of COPD. This is because symptoms often do not appear until after the condition has progressed.

According to the research article, spirometry can lead to an early diagnosis because it shows evidence of COPD before any symptoms appear. The earlier a person receives a diagnosis, the sooner a doctor can optimize treatment.

If a person’s spirometry test indicates that they have COPD, the most important thing they can do is quit smoking and take steps to avoid secondhand smoke, according to the Centers for Disease Control and Prevention (CDC).

Doctors also recommend pulmonary rehabilitation, which is a personalized program involving diet, exercise, and energy conservation techniques.

In addition, the CDC lists the following medication options for treatment:

  • Bronchodilators: These relax muscles in the airways, which opens them and makes it easier for a person to breathe.
  • Steroids: These reduce swelling in the airways.
  • Antibiotics: These treat respiratory infections.

Some treatments for severe COPD include oxygen therapy and surgery. Oxygen therapy helps people with severe COPD, who have low oxygen levels, breathe better. Surgery may involve a lung transplant or the removal of the diseased parts of the lung.

When a person has respiratory symptoms and a compatible medical history, a doctor may use spirometry to help diagnose COPD.

Spirometry also shows how the person’s COPD is progressing. This, along with symptom and exacerbation history, helps guide doctors in their treatment recommendations.