ANTINUCLEAR ANTIBODIES (ANA) - serum

---

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; positive in other systemic rheumatic diseases and with certain drugs.

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 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 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 necessarily reflect disease activity. ANA patterns have limited correlation with specific syndromes, eg anticentromere antibodies are characteristic of the CREST syndrome; rim pattern suggests SLE. Specificity of the antibody for antigenic determinants is established by other tests. See EXTRACTABLE NUCLEAR ANTIGEN (ENA) ANTIBODIES , DNA ANTIBODIES , HISTONE ANTIBODIES .

Reference: Mongey AB et al. Adv Intern Med 1991; 36: 151-169.

---