Upon hearing about the symptoms, a health care provider, whether a primary care provider or emergency department clinician, will formulate a list of possible diagnoses. He or she will ask questions about the symptoms; medical and surgical history; smoking and work history; and other questions about lifestyle, overall health, and the medications taken.
Unless severe hemoptysis is occurring, a chest x-ray will most likely be performed first to look for a cause of the respiratory symptoms.

The x-ray film may or may not show an abnormality.
Types of abnormalities seen in lung cancer include a small nodule or nodules or a large mass.
Not all abnormalities are cancers. For example, some people develop scarring and calcium deposition in their lungs that may look like tumors on a chest x-ray film.

In most cases, a CT scan or MRI of the chest will further define the problem.

If symptoms are severe, the x-ray may be skipped and a CT scan or MRI is performed right away.
The advantages of CT scan and MRI are that they show much greater detail than x-ray film and are in 3 dimensions.
These tests help determine the stage of the cancer by showing the size of the tumor or tumors.
They can also help identify spread of the cancer into regional lymph nodes or certain other organs.

If a person's chest x-ray film or scan suggests that a tumor is present, he or she will undergo a procedure for diagnosis.

This procedure involves removal of a small piece of the tumor tissue (biopsy) or a small volume of fluid from the sac around the lung.
The retrieved cells are reviewed under a microscope by a doctor who specializes in diagnosing diseases by looking at cell and tissue types (a pathologist).
Several different ways exist to obtain these cells.

Sputum testing: This is a simple test that is sometimes performed to detect cancer in the lungs.

Sputum is thick mucus that may be produced during a cough.
Cells in the sputum can be examined to see if they are cancerous. This is called cytologic review.
This is not a completely reliable test. If negative, the findings usually need to be confirmed by further testing.

Bronchoscopy: This is an endoscopic test, meaning that a thin, flexible, lighted tube with a tiny camera on the end is used to view organs inside the body.

Bronchoscopy is endoscopy of the lungs. The bronchoscope is inserted through the mouth or nose and down the windpipe. From there, the tube can be inserted into the airways (bronchi) of the lungs.
The tiny camera transmits images back to a video monitor.
The physician operating the bronchoscope can look for tumors and collect samples of any suspected tumors.
Bronchoscopy can usually be used to determine the extent of the tumor.
The procedure is uncomfortable. A local anesthetic is administered to the mouth and throat as well as sedation to make bronchoscopy tolerable.
Bronchoscopy has some risks and requires a specialist proficient in performing the procedure.