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Sputum stain for mycobacteria

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Sputum test

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Sputum stain for mycobacteria

Definition:

This is a test to check for the presence of Mycobacteria. It involves taking a sputum (what you cough up) sample, staining it so the components become visible, and looking at it under a microscope.

Alternative Names:
Acid fast bacilli stain; AFB stain; Tuberculosis smear; TB smear

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How the test is performed:

Obtain a coughed sputum sample. You are asked to cough deeply and expel any material that comes from the lungs (sputum) into a container. You may be asked to inhale a mist of salty steam in order to cough more deeply and produce sputum. If enough sputum is still not produced, sometimes bronchoscopy will be performed.  

The specimen is spread on a microscope slide. The cells of the specimen are stained with dyes to make the components visible.

The prepared specimen is then examined under the microscope. If the stain shows mycobacteria, the specimen may be placed in culture media, which encourages them to grow. (Specimens are often cultured even if no mycobacteria are seen, since sometimes the number of organisms is so low that they don't show up with staining, but eventually grow on the culture medium.)

How to prepare for the test:

It can help to drink a lot of fluids the night before the test. It enhances the accuracy of the test if done first thing in the morning.

How the test will feel:

There is no discomfort, unless a bronchoscopy needs to be performed.

Why the test is performed:

The test is performed when tuberculosis or other Mycobacterium infection is suspected.

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