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Sputum direct fluorescent antibody (DFA)

Sputum direct fluorescent antibody (DFA) is a test that looks for microorganisms in lung secretions.

Alternative Names

Direct immunofluorescence test; Direct fluorescent antibody - sputum

How the test is performed

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.

How to prepare for the test

If coughing does not produce sputum, a breathing treatment may be given before the test to trigger sputum production.

How the test will feel

There is no discomfort.

Why the test is performed

Your doctor may order this test if you have signs of certain lung infections or pneumonias.

Normal Values

Normally, there is no antigen-antibody reaction.

What abnormal results mean

Abnormal results may be due to an infection such as Legionnaire's disease , mycoplasma pneumonia , or chlamydia pneumonia.

What the risks are

There are no risks.

References

Limper AH. Overview of pneumonia. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 97.

Updated: 5/28/2012

David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.


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