Sputum direct fluorescent antibody (DFA)
Sputum direct fluorescent antibody (DFA) is a test that looks for microorganisms in lung secretions.
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. (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.
Normally, there is no antigen-antibody reaction.
What Abnormal Results Mean
There are no risks.
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.