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Sputum stain for mycobacteria

Definition

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 asked to cough deeply and spit the substance that comes up from the lungs (sputum) into a container.
  • You may be asked to breathe in a mist of salty steam. This makes you cough more deeply and produce sputum.
  • If you still do not 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 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 is done first thing in the morning.

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 Results

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

Risks

There are no risks, unless bronchoscopy is performed.

Considerations

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

More sophisticated tests are sometimes used to stain sputum for mycobacteria. Check with your health care provider to see if these are available in the laboratory.

References

Murray PR. The clinician and the microbiology laboratory. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglass, and Bennett's Principles and Practice of Infectious Diseases. 6th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 16.

Septimus EJ. Pleural effusion and empyema. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglass, and Bennett's Principles and Practice of Infectious Diseases. 6th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 70.


Review Date: 11/24/2014
Reviewed By: Daniel Levy, MD, PhD, Infectious Diseases, Lutherville Personal Physicians, Lutherville, MD. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
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