Bronchitis is an inflammation of the airways in the lungs, typically caused by a viral or bacterial infection. To diagnose bronchitis, a doctor will typically perform a physical exam, review the patient's medical history, and order a series of tests, such as a chest X-ray, pulmonary function tests, blood tests, or sputum culture. During the physical exam, the doctor will listen to the patient's lungs for wheezing or other signs of infection. The patient may also be asked to provide a sputum sample. The results of the tests will help the doctor diagnose the condition and determine the best course of treatment.