DIF stands for direct immunofluorescence. It is a laboratory test that pathologists use to look for specific proteins in a tissue sample. Unlike most tissue samples, which are examined under ordinary light, DIF samples are examined under fluorescent light, which makes the proteins of interest glow so the pathologist can see exactly where they are located. DIF is most commonly performed on skin and kidney biopsies. DIF is a test that helps make a diagnosis; it is not a diagnosis on its own. This article explains how DIF works, why it is done, and what its results can show.
How does direct immunofluorescence (DIF) work?
DIF uses special antibodies that have been tagged with a fluorescent dye. When these tagged antibodies are applied to a tissue sample, they attach to the specific protein they are designed to find, if that protein is present. Under a fluorescence microscope, the dye glows, often bright green, showing the pathologist exactly where the protein is located and in what pattern. The word “direct” means that the fluorescent antibody is applied directly to the patient’s own tissue sample. This is different from immunohistochemistry, another protein test that is read under ordinary light rather than fluorescent light.
Why is DIF performed?
DIF is especially useful for diagnosing conditions in which the body’s immune system deposits proteins, such as antibodies, in a tissue. The location and pattern of these deposits help tell one condition from another. DIF is most often used in two areas:
- Skin biopsies — DIF helps diagnose autoimmune blistering diseases such as pemphigus and pemphigoid, and connective tissue diseases such as cutaneous lupus erythematosus. These conditions can look similar under ordinary light, and the pattern of protein deposits seen with DIF helps separate them.
- Kidney biopsies — DIF helps diagnose diseases of the kidney’s filtering units (the glomeruli), such as IgA nephropathy and membranous glomerulonephritis. The type of protein deposited and its pattern help classify the specific kidney disease.
What kind of sample does DIF need?
DIF usually requires fresh tissue that has not been placed in the standard preservative (formalin) used for most biopsies. That is because formalin can destroy the proteins DIF is designed to detect. For this reason, tissue for DIF is often frozen or placed in a special transport solution. In some cases, this means a separate piece of tissue is taken, or the biopsy is handled differently, so that both routine examination and DIF can be performed. If you had an extra biopsy or special instructions, this may be why.
How are DIF results reported?
A DIF report usually lists which proteins were found and describes the pattern and location of the deposits. The proteins tested for most often are immunoglobulins (antibodies such as IgG, IgA, and IgM), a group of immune proteins called complement (for example, C3), and fibrinogen. The pattern is often described as linear (a smooth, continuous line) or granular (scattered dots or clumps), and the location tells the pathologist which part of the tissue is involved. Together, the proteins present, their pattern, and their location help point to a specific diagnosis. A result may also be reported as negative, meaning none of the tested proteins were found in an abnormal pattern.
Questions to ask your doctor
- Why was direct immunofluorescence (DIF) ordered on my biopsy?
- What condition is the DIF test being used to look for?
- Which proteins were found, and in what pattern?
- Did the DIF result confirm a diagnosis, or is more testing needed?
- Did I need a separate or specially handled biopsy for this test, and why?
- How do the DIF results fit with the rest of my pathology report?
- What are the next steps based on these results?
Related articles on MyPathologyReport.com
We are proud to partner with:
