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Sputum stain for mycobacteria

Sputum stain for mycobacteria is a test to check for a type of bacteria that cause tuberculosis and other infections.

Alternative Names

Acid fast bacilli stain; AFB stain; Tuberculosis smear; TB smear

How the test is performed

This test requires a sample of sputum.

  • To do this, you will be be asked to cough deeply and spit the substance that comes up from the lungs (sputum) into a container.
  • You may be asked to breath in a mist of salty steam. This makes you cough more deeply and produce sputum.
  • If you still don't produce enough sputum, you might have a bronchoscopy .

The test sample is examined under a microscope. Another test, called a culture, is done to confirm the results. A culture test takes a few days to get results. This sputum test can give your doctor a quick, early answer.

How to prepare for the test

It can help to drink a lot of fluids the night before the test. It makes the test more accurate if it's 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 the doctor suspects tuberculosis or other Mycobacterium infection.

Normal Values

Results are normal when no mycobacterial organisms are found.

What abnormal results mean

Abnormal results show that the stain is positive for:

  • Mycobacterium tuberculosis
  • Mycobacterium avium-intracellular
  • Other mycobacteria or acid-fast bacteria

What the risks are

There are no risks, unless bronchoscopy is performed.

Special considerations

To increase the accuracy of this test, it is sometimes done three times, often three days in a row.

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.

References

Septimus EJ. Pleural effusion and empyema.In: Mandell GL, Bennett JE, Dolin R, eds.Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2009:chap 65.

Murray PR, Witebsky FG. The clinician and the microbiology laboratory. In: Mandell GL, Bennett JE, Dolin R, eds.Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2009:chap 17.

Updated: 12/6/2011

David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Jatin M. Vyas, PhD, MD, Instructor in Medicine, Harvard Medical School, Assistant in Medicine, Division of Infectious Disease, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.


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