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Sputum direct fluorescent antibody (DFA)

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

How the Test is Performed

You will produce a sputum sample from your lungs by coughing up mucus from deep inside your lungs. (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 Results

Normally, there is no antigen-antibody reaction.

What Abnormal Results Mean

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


There are no risks.

Alternative Names

Direct immunofluorescence test; Direct fluorescent antibody - sputum


Croft AC, Woods GL. Specimen collection and handling for diagnosis of infectious diseases. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 63.

Pitt BS, Yao JDC. Microbiologic diagnosis of lower respiratory tract infection. In: Mason RJ, Murray JF, Broaddus VC, et al., eds. Murray and Nadel's Textbook of Respiratory Medicine. 5th ed. Philadelphia, PA: Elsevier Saunders; 2010:chap 18.

Update Date 5/29/2014

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