Laboratory Tests - Diagnosing Copd: Respiratory Health

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Laboratory tests

If you have COPD, or if your doctor suspects you do, your doctor might order several laboratory tests. Most of these tests measure oxygen and other details of blood chemistry that can refine the diagnosis and help determine how much the disease has impaired your lungs' ability to take up oxygen and eliminate carbon dioxide.

Alpha-1-antitrypsin. This blood test measures alpha-1-antitrypsin, also called alpha-1-antiprotease. A low level of this substance, which neutralizes the destructive proteases that cause emphysema, may indicate a genetic predisposition to developing emphysema (see "Genetic factors"). Doctors often recommend this test for patients who have a family history of emphysema, who developed emphysema at a relatively young age (younger than 45–50 years), or who have fairly severe emphysema and have not smoked heavily enough in their lives to bring about such severe disease. In addition to checking the level of alpha-1-antitrypsin, doctors can also do a test to determine your genetic type of alpha-1-antitrypsin.

Pulse oximetry. This painless test to measure oxygen saturation in your blood is sometimes called "pulse ox" or "O₂ sat." The doctor places a probe on your finger that shines a beam of light through the finger. Based on how much of the light is absorbed as it passes through the finger, the doctor can determine whether the oxygen level in your blood is normal or too low. If it is very low, the doctor might recommend that you have oxygen therapy. The doctor might also check your oxygen level while you are walking or exercising to see if it falls with activity.

Arterial blood gas. This test looks at how much oxygen and carbon dioxide are in your blood. Although it is more accurate and gives more information than pulse oximetry, it is done less frequently because it requires taking a blood sample from an artery, usually in your wrist. This test is done primarily if you have severe symptoms of COPD or if your condition has worsened. If you are ill with potentially life-threatening carbon dioxide levels, you may need to be not only hospitalized, but also put on a ventilator to help you breathe.

Exercise tests. These include the six-minute walk test and the cardiopulmonary exercise test. As the name suggests, the six-minute walk test evaluates how far you can walk in six minutes, and it also accounts for any difficulty breathing or fatigue you may feel during the test. This test is often conducted before and after you start a new therapy to see how you've responded to the treatment.

Cardiopulmonary exercise testing is more intensive, requiring you to run on a treadmill or ride a stationary bike until you can't do it any more. This test provides specific information on how your heart, lungs, and muscles are working. Your doctor may use this test when he or she suspects that your disease may also involve your heart.

Other tests. If you appear to have an illness other than COPD, your doctor will probably recommend additional tests. For example, if you have pneumonia, the doctor may take a sputum culture to identify the bacteria that are causing it.

Last updated:	May 23, 2007