Chronic obstructive pulmonary disease, also commonly known as COPD, refers to a host of progressive lung disorders that make breathing difficult. About 65 million people worldwide suffer from mild to severe COPD and an estimated 12 million more are living with it unaware. Smoking tobacco is among one of its leading causes, though long-term exposure to chemical irritants can also lead to COPD. Tests that help in diagnosing the condition include lung (pulmonary) function tests, CT scan, chest X-ray, arterial blood gas analysis and some other laboratory tests.