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.

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.

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

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

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

Review Date: 12/01/2009
Reviewed By: Reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc., and Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School, Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)