What are antinuclear antibodies (ANA)?

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%).