Acid-fast stain
Definition
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 (TB) and other illnesses.
How the Test is Performed
Depending on where the infection may be in your body, your health care provider will collect one of these samples:
- Urine
- Stool
- Sputum
- Bone marrow
- Tissue
The sample is then sent to a laboratory. Some of the sample is placed on a glass slide, stained, and heated. The cells in the sample hold onto the dye. The slide is then washed with an acid solution and a different stain is applied.
Bacteria that hold onto the first dye are considered "acid-fast" because they resist the acid wash. These types of bacteria are associated with TB and other infections.
How to Prepare for the Test
Preparation depends on how the sample is collected. Your provider will tell you how to prepare.
How the Test will Feel
How much discomfort you may feel depends on how the sample is collected. Your provider will discuss this with you.
Why the Test is Performed
The test can tell if you are likely infected with the bacteria that cause TB and related infections.
Normal Results
A normal result means no acid-fast bacteria were found on the stained sample.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test result.
What Abnormal Results Mean
Abnormal results may be due to:
- TB
- Leprosy
- Nocardia infections (also caused by a bacteria)
Risks
Risks depend on how the sample is collected. Ask your provider to explain the risks and benefits of the medical procedure.
References
Patel R. The clinician and the microbiology laboratory: test ordering, specimen collection, and result interpretation. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 16.
Rodino KG, Woods GL, Wengenack NL. Mycobacteria. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 59.
Review Date:11/23/2021
Reviewed By:Jatin M. Vyas, MD, PhD, Associate Professor in Medicine, Harvard Medical School; Associate in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997-A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
The Agency for Health Care Administration (Agency) and this website do not claim the information on, or referred to by, this site is error free. This site may include links to websites of other government agencies or private groups. Our Agency and this website do not control such sites and are not responsible for their content. Reference to or links to any other group, product, service, or information does not mean our Agency or this website approves of that group, product, service, or information.
Additionally, while health information provided through this website may be a valuable resource for the public, it is not designed to offer medical advice. Talk with your doctor about medical care questions you may have.
Health Outcome Data
No data available for this condition/procedure.