ANTI-NUCLEAR ANTIBODIES

CLINICAL UTILITY:

Anti-Nuclear Antibodies (ANA) are antibodies which react with nuclear components of cells. Among the nuclear antigens to which antibodies react are DNA, RNA, nucleoli, histones and non-histone proteins. Found in patients with a variety of diseases, ANAs also occur in low titers in about 5% of the normal population, with higher prevalence in the elderly. Most patients with active systemic lupus erythematosus (SLE) have positive ANAs, usually of high titer (1:160 or greater). ANAs often appear also in other rheumatic diseases, and occasionally in a variety of other conditions. If a positive ANA is present, further testing may be indicated to identify the antibody present. Since specific anti-nuclear antibodies occur in various diseases, follow-up testing may be indicated, depending upon the ANA titer, the clinical suspicion and the pattern of fluorescence in the ANA test. For example, a high titer ANA speckled pattern may be associated with antibodies to extractable nuclear antigens (ENA). The ENA antibody test may be helpful if connective tissue diseases are suspected, and aid in differentiation between various diseases in this category.

By ordering the ANA Reflexive Panel, follow-up tests (DNA-Binding and ENA Screen/Identification) are performed on positive samples, and the test for anti-SSA antibodies is also done.

METHOD DESCRIPTION:

Indirect immunofluorescence is the method used to screen for ANA. All samples are tested on two substrates: HEp-2 tissue culture cells (with enlarged nuclei and numerous dividing cells), and rat liver tissue, which has been the substrate classically used for ANA testing. The patterns of fluorescence (homogeneous, speckled, nucleolar, rim or centromere) are reported from both cell types. The titer is reported on rat liver tissue. The screen on rat liver is performed at a dilution of 1:40, and positives titered to 1:640. Further titering on rat liver or HEp-2 cells will be done at the physician’s request.

REFERENCE RANGE:

Negative. About 5% of a normal reference population has a positive ANA test. Most of these have only low ANA titers, i.e. 1:40. A higher prevalence of positive ANA tests is seen in older, apparently normal populations, especially in females. About 15% of women over age 50 have positive ANA tests. Most of these are positive at low titers (1:40), but some older women have ANA titers as high as 1:160.

SPECIMEN REQUIREMENTS:

0.5 ml serum. Freeze.