Synonyms: ANA
Related tests: anti-DNA, ENA, LE test
Clinical significance
Systemic autoimmune diseases are conditions linked to faulty regulation of the mechanisms that control immune tolerance, characterised by the production of antibodies against tissues that are no longer recognised as “self”. ANA are autoantibodies directed against components of the cell nucleus.
The reference method for detecting them is indirect immunofluorescence using HEp-2 cells (human epithelioma type 2 cells) as the substrate, cultured cells with a large nucleus and many nucleoli.
In screening for autoimmune diseases, ANA testing is the first step, alongside clinical assessment. As well as showing that ANA are present, it is important to titrate them (high titres are more clinically significant) and describe the pattern, i.e. the appearance of the fluorescence on the slide.
The main patterns are:
homogeneous (diffuse, uniform fluorescence of the whole nucleus in interphase, while in mitosis the chromosomes fluoresce intensely);
nuclear membrane (fine, linear fluorescence of the nuclear membrane);
speckled (granular fluorescence of the nucleus in interphase);
nucleolar (intense fluorescence of the nucleoli);
centromere (fluorescence of the centromeres in mitosis).
Clinical indications
Systemic autoimmune diseases (systemic lupus erythematosus, scleroderma, Sjögren’s syndrome, polymyositis, dermatomyositis, mixed connective tissue disease).
Sample type
The patient must have a blood sample taken.
Preparation
You must fast for at least 8 hours; a small amount of water is allowed.
Notes
Low-titre ANA may be found in people without autoimmune diseases, especially elderly people (20-25%). Viral infections (mononucleosis, HIV), cancers (lymphomas, myelomas), kidney disease and medicines (procainamide, hydralazine, isoniazid, chlorpromazine, beta-blockers) can cause a positive result.
A titre of 1/80 to 1/160 is considered weakly positive; without significant clinical findings, the result should be monitored over time. Titres above 1/160 should be considered positive.
Detection and titration of ANA are mainly of diagnostic value, while they seem less significant for prognosis and follow-up of the disease.