Antinuclear Ab

Keywords: Antinuclear antibody, Nuclear Ab, Antinuclear factor, ANA, ANF

Specimen:

5 mL blood in plain tube.

Method:

Indirect IF.

Reference Interval:

Depends on age.

Titres are not necessarily comparable between laboratories.

Application:

Diagnosis of SLE and other systemic rheumatic diseases.

Interpretation:

A highly sensitive test for the diagnosis of SLE, being positive in >95% of patients. The specificity of ANA is, however, low.

It is also positive in up to 70% of other systemic rheumatic conditions, often at high titre.

It may also be positive, usually in low titre, in other inflammatory and neoplastic diseases and in a proportion of the normal population, with the prevalence increasing with age.

Higher titres usually have greater diagnostic significance, particularly in younger patients.

Use of the ANA by itself as a screening test should be avoided, as interpretation is difficult in the absence of features suggestive of a systemic rheumatic disease.

Titres often remain elevated in remission and do not reflect disease activity.

ANA patterns have limited correlation with specific syndromes, eg, anticentromere antibodies are characteristic of the CREST syndrome (limited scleroderma); rim pattern suggests SLE. DFS70 pattern may indicate less likelihood of systemic rheumatic disease.

Specificity of the antibody for antigenic determinants is established by other tests.

See Extractable nuclear antigen Ab, DNA Ab and Histone Ab.

Reference:

Solomon DH et al. Arthritis Rheum 2002; 47: 434-444.