Obtain a coughed sputum sample. You are asked to cough deeply and expel any material that comes from the lungs (sputum) into a container. If sputum is not produced, sometimes bronchoscopy will be performed.

The specimen is spread on a microscope slide, which is called a smear. The cells of the specimen are stained with a dye, carbol-fuchsin, heat and acid are applied, and then it is counterstained with methylene blue.

The prepared specimen is then examined under the microscope. If the stain shows mycobacteria, the specimen may be placed in culture media. (Specimens are often cultured even if no mycobacteria are seen, since sometimes the numbers are so low that it is hard to see them.)

To increase the accuracy of this test, it is sometimes done three times, often on three consecutive days.

There are more sophisticated tests that are sometimes used to stain sputum for mycobacteria. Check with your health care provider to see if these are available in the laboratory.