Immunofluorescence and the ANA test !
- Topic
The ANA test looks for antibodies against the nucleus of the body's own cells. It is read with a fluorescence microscope and points toward autoimmune disease.
Updated 2026-11-01
What it is
In immunofluorescence, an antibody tagged with a fluorescent dye shows where antibodies bind. For antinuclear antibodies (ANA), serum is incubated on HEp-2 cells and the titer and nuclear staining pattern are reported. A negative ANA makes lupus very unlikely, but a positive ANA alone diagnoses nothing.
Key facts
- ANA is very sensitive for lupus (positive in almost all) but not specific.
- The most lupus-specific antibodies are anti-double-stranded DNA and anti-Sm.
- Low titers occur in healthy people, especially older women, and in viral infections.
- Some drugs (procainamide, hydralazine, isoniazid) induce ANA and anti-histone antibodies.
ANA patterns and classic associations
| Pattern | Typical antibodies | Association |
|---|---|---|
| Homogeneous | Anti-double-stranded DNA, anti-histone | Lupus; drug-induced lupus (anti-histone) |
| Speckled | Anti-Sm, anti-RNP, anti-Ro, anti-La | Lupus, mixed connective tissue disease, Sjögren |
| Centromere | Anti-centromere | Limited systemic sclerosis (CREST) |
| Nucleolar | Anti-Scl-70 or other nucleolar antibodies | Diffuse systemic sclerosis |
In the lab
- Indirect immunofluorescence: patient serum + reference cells or tissue + fluorescent anti-immunoglobulin. Used for ANA and ANCA.
- Direct immunofluorescence: patient biopsy + fluorescent anti-immunoglobulin; in kidney and skin it shows where deposits sit.
- Linear pattern (anti-glomerular basement membrane, pemphigoid) versus granular (immune complexes, as in lupus nephritis).
- The titer is reported as a dilution (1:80, 1:160…); many labs take 1:160 or higher as significant.
Test yourself
Think of the answer, then tap the question to see it.
Which two autoantibodies are most specific for systemic lupus erythematosus?
Anti-double-stranded DNA and anti-Sm.
Which antibody suggests drug-induced lupus?
Anti-histone antibodies, with a homogeneous ANA pattern.
Which ANA pattern goes with limited systemic sclerosis (CREST)?
The centromere pattern, from anti-centromere antibodies.
What is the difference between direct and indirect immunofluorescence?
Direct looks for antibodies already deposited in the patient's tissue; indirect looks for antibodies in the patient's serum on reference cells or tissue.
Related
- Serology: IgM vs IgG, seroconversion, avidity
- Direct and indirect Coombs test
- Flow cytometry and the CD4 count
- Autoantibodies: the table to know
- Type III hypersensitivity (immune complexes)
Related conditions
Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.
Sources: ANA (Antinuclear Antibody) Test (MedlinePlus (U.S. National Library of Medicine), 2024); Antinuclear antibody panel (MedlinePlus (U.S. National Library of Medicine), 2024).
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Representative model, for educational purposes only.