Antinuclear antibodies (ANA) are autoantibodies which have failed to
recognise self and are produced in an autoimmune response. These can be IgG, IgA or IgM but only IgG are
considered clinically significant. Due to the cellular location of
the antigens a number of patterns can be produced. These can be divided into nuclear, cytoplasmic or cell cycle related and are reported accordingly.
Patient serum is diluted 1:40 (some laboratories use 1/80 dilution) and
incubated with HEp2 cells fixed on glass slides and then fluorescence
labelled antihuman-IgG antibodies are added to detect any patient
antibodies which have bound to the HEp-2 cells. The extent of staining
is determined by dilution of serum (1:100, 1:400 and 1:1600) in order to
establish the endpoint. The antibody patterns and the titres (ie the
dilution at which the staining was still visible) are reported.
Requesting ANA?
ANA can be present in up to 20% of the population with a low/medium
titre (i.e. 1:40 - 1:400) particularly in people over the age of 50. ANA
can also appear transiently following major or minor illness. The
specificity of the test therefore reflects the clinical picture of the
patient and is most useful in patients with suspected autoimmune
disease.
How is ANA is tested?
Human Epithelial cell line type 2
(HEp2) is commonly used for screening ANAs.
Clinical
significance of a positive ANA?
• Low titre ANAs (ie 1:40 or 1:100) - usually not clinically relevant.
• High titre ANA (particularly 1:1600) - greater clinical significance
is attributed to these.
ANA is associated with clinical
condition such as systemic lupus erythematosus (SLE) (95%), drug induced
lupus (90%), mixed connective tissue (95%), Sjögren's syndrome (80%),
scleroderma (90%) and polymyositis/dermatomyositis (40%).
