As mentioned earlier, smoking can cause many diseases including lethal ones like lung cancer. To detect smoking-related diseases the following tests may be recommended:

Imaging tests:

An X-ray or CT scan can reveal lesions, or abnormal nodule or mass in the lungs which may be a sign of lung cancer.

Sputum cytology:

Your sputum may be checked under the microscope to do detect lung cancer cells or other indication of disease.

Tissue sample (biopsy):

There are many methods of doing a biopsy of abnormal cells which can help to detect diseases.