Common Diagnostic Tests for COPD

Chronic Obstructive Pulmonary Disease or COPD refers to both chronic bronchitis and emphysema. These two illnesses obstruct the airways and lower oxygen levels. Diagnostic tests are necessary to tell the two conditions apart although generic tests are used to determine if a patient has COPD in the first place.

Test #1 - Spirometry

Spirometry measures the capacity of the lungs using air-time measurements. The test measures the air that a person exhales. The three variables that are measured are FEV1 (forced expiratory volume after one second), FVC (forced vital capacity), and FEF25-75 (forced expiratory flow at 25% to 75%). If the patient has 70% or less volume than a healthy person, he probably has COPD.

Doctors may do this test several times and in a different format called a post-bronchodilator test where a bronchodilator is used prior to the test so the patient's airways are relaxed and expanded. This can tell doctors if the lung capacity can be reversed

Test #2 - Measuring Lung Volume

Doctors also measure lung volume using gas dilution or plethysmography. Lung dilution involves inhaling nitrogen or helium and measuring the gas volume to determine lung volume. Body plethysmography requires the patient getting into an airtight chamber and breathing in and out through a tube. The air volume is measured as pressure changes in the chamber to determine the approximate lung volume of the patient. These tests results are going to be adjusted based on a patient's height, age, and other factors so that the patient can be compared to similar people with healthy lungs.

Test #3 - Diffusion Capacity

Diffusion capacity measures how well the alveoli (small sacs on the end of the airways) allow gas exchange to take place in the lungs. The patient breathes in a little bit of carbon monoxide, a safe amount, and then blood samples are taken to measure how much was passed into the body. This test can detect emphysema.

Test #4 - Oximetry

In order to diagnose COPD, doctors need to determine how much oxygen is in the bloodstream. This can be done several ways. One test measures oxygen content in arterial blood but removing blood from the arteries can be very painful so oximetry is an alternative that is used in many cases. Oximetry involves shining light through the thumb and measuring the light that comes out the other side. This measurement can tell doctors what the oxygen levels are without drawing blood but it is not as accurate as actual blood tests.