ENA Blottest
ENA Blot Test : (ENAB) serum Extractable Nuclear Antigen antibodies, fluorescent antinuclear antibody test, FAN, antibodies to extractable nuclear antigen,
consisting of:
- CENP-B (centromeres)
- ds-DNA
- histones
- Jo-1
- nucleosomes
- PCNA
- PM Scl
- ribosomal P-protein
- nRNP/Sm €
- Scl-70
- Sm
- SS-A (Ro)
- SS-A (Ro-52)
- SS-B (La)
The test measures antibodies to nuclear antigens. These are antibodies directed against nuclei (nucleus) of the body's own cells. The ENA test can be used to examine whether the body produces antibodies against itself.
The immune system produces these so-called auto-antibodies (auto meaning self) when it fails to distinguish between its own cells and foreign cells. Production of autoantibodies can lead to autoimmune diseases. These diseases are usually accompanied by inflammation and all that goes with it: fever, pain and fatigue.
Examples of these nuclear antibodies include anti-nRNP, anti-Sm, anti-SSA/Ro, anti SSB/La, Scl-70 Jo-1 and anti-CEN-P.
The different antibodies can be found in autoimmune diseases such as SLE (systemic lupus erythematosus), Sjögrens syndrome, MCTD (mixed connective-tissue disease), CREST syndrome, polymyositis or dermatomyositis. The occurrence of the different types of antibodies varies by disorder.
A positive result means that autoantibodies have been detected. This may indicate an autoimmune disease, but not necessarily. Especially in older people, it can happen that autoantibodies are shown, without the presence of an autoimmune disease. In healthy elderly people (>65 years), the false positive rate can be as high as almost 40%.
The use of some medications can also lead to the production of autoantibodies even though there is no autoimmune disease.
A negative result (no antibodies detected) makes some autoimmune diseases unlikely. But it happens (about in 5% of cases) that a person does have an autoimmune disease but does not produce autoantibodies. Given the variable nature of SLE, for example, there is no harm in repeating the test later if it is suspected.
