To diagnose chronic obstructive pulmonary disease (COPD) for sure, a doctor needs to order pulmonary (lung) function tests. These are special tests that provide measurements of:
- How much air a person's lungs can hold (the "forced vital capacity," or FVC).
- How quickly the person can breathe out (the "forced expiratory volume in one second," or FEV1).
In COPD, FEV1 is lower than normal, and FVC is often higher than normal.
Doctors often take a chest X-ray or CT scan in people who complain of shortness of breath. Although this is reasonable, to diagnose COPD it's also necessary to do the pulmonary function testing.
Another test doctors may use is a special blood draw called an ABG (arterial blood gas). People with COPD usually have higher-than-normal levels of carbon dioxide in the blood. In more advanced COPD, they also develop lower-than-normal levels of oxygen in the blood. The ABG draw measures these levels to help determine the disease's severity. (An oxygen saturation meter, which clips onto the finger, measures oxygen but doesn't provide information about carbon dioxide levels.)