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Ency. home > Test > A > Acid-fast stain

Acid-fast stain   

Overview | Risks | Results

Alternative names:

Mycobacterial stain; AFB stain; TB stain

Definition:

The acid-fast stain is a test used to examine a specimen for the presence of microorganisms, specifically mycobacteria which include the bacteria that cause tuberculosis.

How the Test is Performed

A specimen is collected from you. Blood, urine, stool, sputum, bone marrow, or tissue samples may be collected, depending on the location of the suspected infection.

The specimen is then sent to a microbiology laboratory for processing. A small amount of the specimen is placed on a microscope slide. A dye is placed on the slide and heated. The cells retain the dye. The slide is then washed with an acid solution, and a counter-stain is applied.

The bacteria that retain the first dye are acid fast because they resist the acid wash. Bacteria that wash free of the first dye and take the counterstain are nonacid fast.

How to Prepare for the Test

Preparation for the test depends on the sample to be collected. There may be special preparation for a blood, urine, or stool collection. A biopsy of an organ or tissue may be indicated for certain types of infection.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:

How the Test will Feel

The amount of discomfort depends on the type of specimen to be collected. A tissue biopsy or aspiration with a needle may be necessary for some tests.

Why the Test is Performed

The test detects infection caused by mycobacteria. The test is useful in detecting tuberculous infection.

Ency. home > Test > A > Acid-fast stain

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