To find out if lung cancer may be present, the doctor evaluates a person's medical history, smoking history, their exposure to environmental and occupational substances, and family history of cancer. The doctor will also give the patient a physical examination. This is for detecting any signs of cancer such as swollen lymph nodes in the neck or collarbone area. If lung cancer is suspected, a patient must undergo a series of diagnostic tests.

In some people lung cancer doesn't show any symptoms. In such people a method called screening is used to detect the cancer. The two main test used for this are chest x-rays and sputum cytology

Chest x-ray : This is the first test to verify any spot on the lungs. X-rays are plain pictures of the lung, which will help to identify any abnormal growths. If lung cancer is suspected, a simple test called sputum cytology is performed. It is the microscopic examination of cells obtained from a deep-cough sample of mucus in the lungs. The presence abnormal or cancerous (malignant) cells can be discovered by this test.

Not all abnormalities are cancers. Some people develop scarring and calcium deposition in their lungs that may look like tumors on a chest x-ray film. In such cases, to confirm the diagnosis various scanning are prescribed by the specialist.

CT (Computed tomography) or CAT scan : It is a special kind of x-ray which reveal much more than chest x-ray. A CT scan takes a series of x-rays that build up a three-dimensional picture of the inside of the body. It gives a detailed information about the size, shape, and place of a tumor. CT scan helps to determine whether the cancer is in the chest wall and rib area. It also helps to find the enlarged lymph nodes that might contain cancer and the tumors in other organs that might be affected by the spreading of lung cancer.

MRI (Magnetic Resonance Imaging) scan :MRI use radio waves and strong magnets to create an image. This scanning is useful in finding lung cancer, that has spread the brain or spinal cord.

PET (Positron Emission Tomography) scan : PET uses a low-dose radioactive sugar to trace the activity of body cells on sugar. A very small amount of radioactive substance is injected into a vein (usually on hand) and a scan is then taken. Areas of cancer are usually more active than surrounding tissue so they take up more of the radioactive substance and show up on the scan. PET helps to determine whether lung cancer has spread to lymph nodes. It is also helpful in telling whether a spot on your chest x-ray is cancer.

Bone Scans : A bone scan can determine whether the cancer has spread to the bones. It is usually done in patients with small cell lung cancer. A small amount of radioactive substance is injected into a vein and this substance builds up in areas of bone that may be abnormal because of cancer. In patients with non-small cell lung cancer, bone scan is done when other tests or symptoms suggest that the cancer has spread to the bones.

To confirm the presence of lung cancer, the doctor must examine tissue from the lung. This is called biopsy which is the removal of a lung tissue sample for examination under a microscope. Biopsies are obtained in different ways depending on the location of the tumor: They are :

Bronchoscopy : Bronchoscope is a thin, lighted, flexible tube with a tiny camera on the end. This is passed through the mouth or nose and down through the windpipe. From there, the tube can be inserted into the airways (bronchi) of the lungs. Small samples of tissue are collected through this tube. Bronchoscopy, which is used to determine the extent of the tumor, has some risks and requires a specialist proficient in performing the procedure.

Needle biopsy : If a tumor is on the periphery of the lung, it usually cannot be seen with bronchoscopy. After the chest surface is cleaned and prepared, the skin and the chest wall are numbed. A long, thin needle is inserted through the chest wall in the lung to remove a lung tissue sample. A chest x-ray or CT scanning is used to guide the needle.

Thoracentesis : Lung cancers, both primary and metastatic, can cause fluid to collect in the sac surrounding the lung. This is called pleural effusion. Thoracentesis, which is important for both staging and diagnosis, is similar to needle biopsy. The skin is numbed and a needle is placed between the ribs to remove a fluid sample.

Thoracoscopy : It uses a thin, lighted tube connected to a video camera and monitor to view the space between the lungs and the chest wall. It is used to check whether the fluid around the lungs is caused by cancer.

Thoracotomy : Sometimes a lung cancer tumor cannot be reached by bronchoscopy or needle procedures. In such cases the only way to obtain a biopsy is by performing a surgery. The chest is opened and as much of the tumor as possible is removed surgically. A biopsy is taken from the removed tumor. This procedure is a major operation performed in a hospital.

Mediastinoscopy : It is performed to determine the extent that the cancer has spread into the area of the chest between the lungs. A small cut is made into the lower part of the neck, above the breastbone. A mediastinoscope is inserted and sample tissues are taken from the enlarged lymph nodes along the windpipe. Mediastinoscopy is a very important step to determine whether the tumor can be surgically removed or not.

Bone marrow biopsy : After the area is numbed, a needle is used to remove a small piece of bone, usually from the back of the hip bone. This is done mostly to help find if small cell lung cancer has spread to the bones.

Blood tests : Blood tests are performed to identify any chemical imbalances, blood disorders, or other problems that might complicate treatment. A complete blood count (CBC) shows whether your blood has the correct number of different cell types. This test will be done often if you are treated with chemotherapy because these drugs can affect the blood-forming cells of the bone marrow.

Once a tumor is found, it must be determined if and how widely the cancer has spread. It is known as staging.