Definition of Acid-fast stain:

The acid-fast stain is a laboratory test that determines if a sample of tissue, blood, or other body substance is infected with the bacteria that causes tuberculosis and other illnesses.

How the test is performed:

Your health care provider will collect a sample of blood, urine, stool, sputum, bone marrow, or tissue, depending on the location of the suspected infection.

The sample is then sent to a laboratory, where a small amount is placed on a glass slide, stained, and heated. The cells in the sample hold onto the dye. The lab team member washes the slide with an acid solution and applies a different stain.

The bacteria that hold onto the first dye are considered "acid-fast" because they resist the acid wash. This type of bacteria is associated with tuberculosis and other infections.

How to prepare for the test:

Preparation depends on how the sample is collected. Your health care provider will tell you how to prepare.

How the test will feel:

The amount of discomfort depends on how the sample is collected.

Why the test is performed:

The test can tell if you are infected with mycobacteria, the organism that causes tuberculosis and related infections.