Direct immunofluoresence test

Alternative names 
Sputum DFA (direct fluorescent antibody)

This is a test performed to detect the presence of microorganisms in sputum by using antibodies tagged with a fluorescent dye.

How the test is performed
A sputum sample is obtained by coughing into a specimen container. In the laboratory, antibodies that have been chemically linked to a fluorescent dye are added to the sample. The “flagged” antibodies will attach themselves to the specific antigens (in this case, the microorganism against which they were formed). The specific microorganism (antigen) is indirectly identified by the presence of fluorescence when examined under a special microscope.

How to prepare for the test
Obtain a coughed sputum specimen. If there is not a productive cough, a respiratory treatment may produce a sample.

How the test will feel
There is no discomfort.

Why the test is performed
This test may be performed when certain types of pulmonary infections or pneumonias are suspected.

Normal Values
Normally, there is no antigen-antibody reaction. A reaction indicates infection.

What abnormal results mean
Abnormal results may indicate a specific infection depending on the antigens tested. Legionella or Mycoplasma pneumonia are 2 infections that can be determined by this test.

What the risks are
There are no risks.

Johns Hopkins patient information

Last revised: December 2, 2012
by Arthur A. Poghosian, M.D.

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