Sputum Direct Fluorescent Antibody (DFA) Test

Last updated: February 8, 2026 Medically reviewed by: RxHarun Orthopedic Specialist Doctor Reading time: 1 min read

Direct immunofluorescence test; Direct fluorescent antibody – sputum

Sputum direct fluorescent antibody (DFA) is a lab test that looks for micro-organisms 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.)

The sample is sent to a lab. There, a fluorescent dye is added to the sample. If the micro-organism 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 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

Risks

There are no risks with this test

Frequently Asked Questions

Is this article a replacement for a doctor?

No. It is educational content only. Patients should consult a qualified clinician for diagnosis and treatment.

When should I seek urgent care?

Seek urgent care for severe symptoms, rapidly worsening condition, breathing difficulty, severe pain, neurological changes, or any emergency warning sign.

References

Add references, clinical guidelines, textbooks, journal articles, or trusted medical sources here. You can edit this area later with a custom field named _rx_references.

Written by Dr. Harun Ar Rashid, MD - Arthritis, Bones, Joints Pain, Trauma, and Internal Medicine Specialist

Dr. Md. Harun Ar Rashid, MPH, MD, PhD, is a highly respected medical specialist celebrated for his exceptional clinical expertise and unwavering commitment to patient care. With advanced qualifications including MPH, MD, and PhD, he integrates cutting-edge research with a compassionate approach to medicine, ensuring that every patient receives personalized and effective treatment. His extensive training and hands-on experience enable him to diagnose complex conditions accurately and develop innovative treatment strategies tailored to individual needs. In addition to his clinical practice, Dr. Harun Ar Rashid is dedicated to medical education and research, writing and inventory creative thinking, innovative idea, critical care managementing make in his community to outreach, often participating in initiatives that promote health awareness and advance medical knowledge. His career is a testament to the high standards represented by his credentials, and he continues to contribute significantly to his field, driving improvements in both patient outcomes and healthcare practices. Born and educated in Bangladesh, Dr. Rashid earned his BPT from the University of Dhaka before pursuing postgraduate training internationally. He completed his MD in Internal Medicine at King’s College London, where he developed a special interest in inflammatory arthritis and metabolic bone disease. He then undertook a PhD in Orthopedic Science at the University of Oxford, conducting pioneering research on cytokine signaling pathways in rheumatoid arthritis. Following his doctoral studies, Dr. Rashid returned to clinical work with a fellowship in interventional pain management at the Rx University School of Medicine, refining his skills in image-guided joint injections and minimally invasive pain-relief techniques.