The fluorescence test for ANA is performed by incubating the patient’s serum with a fixed monolayer of human larynx epithelioma cancer (HEp-2) cell lines. If ANAs are present in the serum, they bind to the nuclear component of the substrate. Next, fluorescent anti-Ig is added, which binds to antibodies (if present) in the test serum. With the fluorescent tag, the ANA can be directly visualized under fluorescent light. Different patterns of staining occur, and although they may provide some information, they do not identify the specific antibody present, nor are they specific for a disease entity. For example, the rim or peripheral pattern (usually associated with antibodies directed against nuclear membrane proteins) may be obscured if another autoantibody (staining a homogeneous pattern) is present.
Adapted from von Mühlen CA, et al: Autoantibodies in the diagnosis of systemic rheumatic diseases. Semin Arthritis Rheum 24:323-358, 1995.