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Definition:
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Sputum direct fluorescent antibody (DFA) is a test that looks for microorganisms in lung secretions.
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Alternative Names:
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Direct immunofluorescence test; Direct fluorescent antibody - sputum
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How the test is performed:
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You will produce a sputum sample from your lungs by coughing up mucus from deep inside your lungs. (The mucus is not the same as saliva or spit from the mouth.)
In the laboratory, antibodies that have been chemically linked to a fluorescent dye are added to the sample. These antibodies are considered "tagged." They will attach to specific antigens -- in this case, the microorganism against which they were formed. If the specific microorganism is present, a bright glow (fluorescence) can be seen in the sputum sample using a special microscope.
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How to prepare for the test:
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If coughing does not produce sputum, a breathing treatment may be given before the test to trigger sputum production.
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How the test will feel:
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There is no discomfort.
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Why the test is performed:
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Your doctor may order this test if you have signs of certain lung infections or pneumonias.
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Normal Values:
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Normally, there is no antigen-antibody reaction.
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What the risks are:
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There are no risks.
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References:
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Limper AH. Overview of pneumonia. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 97.
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