Diagnostic Tests

In spite of the widespread incidence and seriousness of chronic obstructive lung disease, studies strongly suggest that it is underdiagnosed, especially in women. Some experts recommend that any adult smoker who complains of a daily cough should be screened for COLD. In one 2002 study, nearly half of patients over 60 who regularly smoked had COLD.

Medical and Personal History

The doctor will request a history that evaluates the patient's risk factors. Risk factors include past and present smoking, low exercise capacity (e.g., whether the patient has trouble climbing stairs, the distance he or she can walk), and exposure to any industrial pollutants.

Physical Examination

Appearance. The appearance of the patients may be a clue to the condition. Bluish skin tone and swelling in the legs suggest chronic bronchitis. Healthy skin tone, but having an inflated chest, suggests emphysema.

The patient will also be asked to cough and produce sputum, if possible.

Chest Examination. The physician will next perform a simple examination of the chest area. Using a stethoscope, the physician will listen to the patient's breathing:

• Diminished or distant breath sounds are signs of emphysema. Tapping the chest will usually produce a hollow, drum-like sound.
• In chronic bronchitis, the physician is likely to hear wheezing or gurgling sounds.

Pulmonary Function Tests (Spirometry)

The best tests for determining the presence of COLD, and managing its response to treatment, are pulmonary function tests. The most common test is spirometry. Spirometry measures the volume and force of air as it is exhaled from the lungs. The patient is asked to breathe in and to exhale forcefully into an instrument several times. The force of the air is then monitored and measured.

Using the results, the physician determines two important values:

• The forced vital capacity (FVC). FVC is the maximum volume of air that can be exhaled (breathed out) with force, and is an indicator of lung size, elasticity, and how well the air passages open and close.
• The forced expiratory volume in one second (FEV1). FEV1 is the maximum volume of air exhaled in 1 second. Airflow is considered to be limited if the outflow of forced exhalation stays low over the course of one second. Steady but faster than normal decline in FEV1 over time characterizes COLD.
• Calculating a ratio of FEV1 to FVC is the best method for determining the presence and severity of COLD.

Severe COLD is an FEV1/FVC ratio of 34 - 49%, whereas very severe COLD is an FEV1/FVC ratio of less than 34%.

Spirometry is a painless study of air volume and flow rate within the lungs. Spirometry is frequently used to evaluate lung function in people with obstructive or restrictive lung diseases such as asthma or cystic fibrosis.

Tests for Measuring the Ability of the Lung to Exchange Gases

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 are often indicative of chronic bronchitis, but not always of 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, which can be painful.

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 a pulse oximetry, which involves placing a probe on the finger or ear lobe. The probe emits two different lights, and 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, indicated by 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.

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 COLD. By the time an x-ray reveals the disease, the patient is well aware of the condition.

Clear signs of emphysema include the following:

• A flattened diaphragm
• Exaggerated lung inflation in upper areas
• Abnormally large amounts of air spaces in the lung
• A smaller heart; if heart failure is present, however, the heart size becomes normal and signs of overinflated lungs are not present.
• A1AD-related emphysema patients show larger amounts of air in the lower lungs

Chest x-rays are rarely useful for diagnosing chronic bronchitis, although they sometimes show mild scarring and thickened airway walls.

Computed Tomography. Computed tomography (CT) scans can accurately assess the severity of COLD and may be used to determine the size of the air pockets (bullae) in the lungs. This imaging technique may even be useful for assessing mild COLD.

Other Tests for Chronic Obstructive Lung Disease

Noninvasive Methods for Determining Severity. Questionnaires and short exercise tests are very useful for determining the severity of COLD.

Test for ATT. Physicians will typically test for the protective enzyme, alpha 1-antiprotease (ATT or antitrypsin), which is often deficient in COLD patients (although asthma patients may also have low levels).

Additional Blood and Sputum Tests. Additional tests may be required if the physician suspects other medical problems. If pneumonia is present, for instance, blood and sputum tests and cultures may be performed to determine the cause of infection.

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Review Date: 4/28/2006
Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital