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In order to determine whether your lung problem symptoms are caused by COPD (chronic obstructive pulmonary disease), your doctor will perform a physical examination, take a detailed medical history, ask about any history of smoking (or current smoking habit) and other lifestyle issues, and perform a COPD diagnosis.
The main COPD test methods for checking COPD signs and symptoms (along with asthma and many other lung diseases), are pulmonary function tests.
COPD Diagnosis: How It’s Done
Pulmonary function tests measure the ability of the lungs to hold air, to move air in and out, and to move oxygen into the blood. The values obtained from most pulmonary function tests are expressed in percentages, and are compared to values expected for a person of similar age, height, ethnicity, and gender who does not have any lung disease. This comparison is made because several factors can influence lung function.
One of the most important facts about lungs when it comes to a COPD diagnosis is that lung function decreases as people age even if they don’t have COPD. So it’s important to compare the test values to those of people with similar characteristics. For example, a spirometry reading (see below) may reveal a forced expiratory volume in 1 second (FEV1) of less than 80 percent of predicted for a person of the same age with no lung disease. Such a result indicates impaired lung function, possibly due to COPD, or possibly due to another condition on the lung diseases list (for example, asthma).
In a test called spirometry, the patient takes a deep breath in, and then exhales as hard and as long as possible into a hose connected to a machine called a spirometer. The spirometer can be used to take several types of measurements. Some common ones used in the diagnosis and management of obstructive lung diseases include:
- Forced vital capacity (FVC): The total amount of air that can forcibly be blown out after inhalation.
- Forced expiratory volume in 1 second (FEV1): The amount of air that can be blown out in one second. If you don’t have a high FEV1, COPD could be the problem.
- The ratio of FEV1 to FVC (FEV1/FVC): In healthy adults, this should be 75 to 80 percent.
- Peak expiratory flow (PEF): The speed of air moving out of the lungs at the beginning of an exhalation.
Bronchodilator Reversibility Testing
Another common COPD test is bronchodilator reversibility testing. For this test, the patient does a spirometry test, and then takes a type of drug called a bronchodilator before taking the spirometry test a second time. Bronchodilators open up narrowed airways by loosening the muscles surrounding the airways. If the spirometry test improves after taking a bronchodilator, this suggests that the patient has asthma rather than COPD, since asthma is often reversible. But for people with COPD, airflow will continue to be limited even after taking the drug.
Peak Flow Meter
A simpler device for measuring how quickly air can be expelled from the lungs is a peak flow meter. Using this handheld device, the person inhales deeply and then blows as hard as possible into the device. If the airways are narrow or blocked, the peak flow will drop below normal. Peak flow meters are generally not recommended for diagnosing lung conditions. Instead, they are used by people with asthma to monitor their condition over time, or to determine how well a particular medication is working.
Measuring Lung Volume
Another type of pulmonary function test measures lung volume. In people with COPD, air often gets trapped in the lungs. Having too much air in the lungs can make the lungs overly inflated (hyperinflated). To determine whether this is happening, a physician may perform one of two tests to measure lung volume:
- Body plethysmograph. In this test, the patient sits in a sealed, clear box and breathes into a mouthpiece connected to a measuring device. Lung volume is determined by changes in pressure inside the box.
- Helium dilution or nitrogen washout. A second method for determining lung volume involves breathing nitrogen or helium gas through a tube. The concentration of the gas in a chamber attached to the tube is measured to estimate the lung volume.
Diffusing Capacity of the Lung for Carbon Monoxide
The destruction of alveoli in people with emphysema can impair the normal exchange of oxygen and carbon dioxide. To estimate how well the lungs are able to move oxygen into the blood, a test called diffusing capacity of the lung for carbon monoxide (DLCO) may be performed. For this test, the patient inhales harmless gas that contains a small amount of carbon monoxide, holds his or her breath briefly, and then rapidly exhales into a tube. The exhaled gas is analyzed to determine how much carbon monoxide was absorbed by the lungs. This provides information about how quickly gas can move from the lungs into the bloodstream.
This test uses sound waves to detect airway changes that indicate obstructive lung diseases such as asthma and COPD. The patient breathes normally into a device that generates vibrations and calculates resistance to breathing.
This technique may be used to diagnose airway disease in very young children, or in older adults with physical or intellectual impairments that make performing spirometry (which involves vigorously exhaling into a machine) difficult or impossible. It also may be used along with spirometry. Some studies suggest that impulse oscillometry may identify COPD earlier than is possible with spirometry.
A chest X-ray generally cannot be used for COPD diagnosis, because only severe emphysema will be visible on a chest X-ray. However, your doctor may have you undergo a chest X-ray to see if your symptoms might be attributable to another condition, such as heart failure or another lung disease.
- Computed tomography: Computed tomography (CT) is another type of imaging study that may be used for some patients. During a CT scan, thin X-ray beams rotate around the patient, creating a series of two-dimensional images. A computer turns these images into a three-dimensional image of the lung (or other organ). This test is better at detecting emphysema than chronic bronchitis or asthma, but CT scanning is not generally used for an initial COPD diagnosis. It may be used to decide if a patient with COPD is a candidate for surgery, or to diagnose another lung disease called bronchiectasis.
- Arterial blood gas test: For patients with advanced COPD, an arterial blood gas test may be performed. This measures the amount of oxygen and carbon dioxide in the blood. It is used to determine whether there is too little oxygen in the blood (a condition called hypoxemia), or to detect the presence of too much carbon dioxide (called hypercapnia).