Table of Contents
Tests for Measuring the Ability of the Lung to Exchange Oxygen and Carbon Dioxide
Arterial Blood Gas. The physician may request an arterial blood gas test to determine the amount of oxygen and carbon dioxide in the blood (its saturation). Low oxygen (hypoxia) and high carbon dioxide (hypercapnia) levels often indicate chronic bronchitis, but not always emphysema. A blood gas analysis that shows very low oxygen levels is useful for determining which patients would benefit from oxygen therapy (see below). This procedure typically involves drawing blood from an artery in the wrist.
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Click the icon to see a depiction of arterial blood gas sampling. |
Pulse Oximetry Test. A safe and painless test for measuring oxygen in the blood is called pulse oximetry, which involves placing a probe on the finger or ear lobe. The probe emits two different lights. The amount of each light the blood absorbs is related to how much oxygen the red blood cells carry. This test measures only oxygen in the blood, however, and not carbon dioxide. Results should be taken together with other tests to determine the need for medication or oxygen therapy.
Carbon Monoxide Diffusing Capacity. The lung carbon monoxide diffusing capacity (DLCO) test determines how effectively gases are exchanged between the blood and airways in the lungs. Patients should not eat or exercise before the test, and they should not have smoked for 24 hours.
The patient inhales a mixture of carbon monoxide, helium, and oxygen and holds his or her breath for about 10 seconds. The gas levels are then analyzed from the exhaled breath. Results can help physicians differentiate emphysema from chronic bronchitis and asthma. Patients with emphysema have lower DLCO results (a reduced ability to take up oxygen). Such results are also important in helping to determine appropriate candidates for lung reduction surgery. Carbon monoxide levels that are 20% or less than predicted values pose a very high risk for poor survival.
Exhaled Breath. The measurement of nitric oxide (NO) in exhaled breath can be a simple method of diagnosing COPD and monitoring the effects of treatment. In most patients with COPD, no levels are below normal. Levels above normal in a patient with COPD indicate that the person also has asthma.
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Click the icon to see an image of lung diffusion testing. |
Imaging Tests
Chest X-Rays. Chest x-rays are often performed, but they are not very useful for detecting early COPD. By the time an x-ray reveals COPD, the patient is already well aware of the condition. X-rays can look for growths in the lungs to rule out other diseases, however.
Clear signs of COPD on x-ray include the following:
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Review Date: 04/10/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine,
Harvard Medical School; Physician, Massachusetts General Hospital.
Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M.,
Inc.
A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)
