Sputum direct fluorescent antibody (DFA) test

Definition

Sputum direct fluorescent antibody (DFA) is a lab test that looks for micro-organisms 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. (Mucus is not the same as saliva or spit from the mouth.)

The sample is sent to a lab. There, a fluorescent dye is added to the sample. If micro-organisms are 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 with this test.

Why the Test is Performed

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

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
• Pneumonia due to certain bacteria, viruses, fungi, or other micro-organisms

Risks

There are no risks with this test.

References

Banaei N, Deresinski SC, Pinsky BA. Microbiologic diagnosis of lung infection. In: Broaddus VC, Ernst JD, King TE, et al, eds. Murray and Nadel's Textbook of Respiratory Medicine. 7th ed. Philadelphia, PA: Elsevier; 2022:chap 19.

Patel R. The clinician and the microbiology laboratory: test ordering, specimen collection, and result interpretation. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 16.