Different markers for different autoimmune diseases
Autoimmune diseases are accompanied by autoantibodies, which sometimes are only seen in this special disease - such autoantibodies can serve as a marker for the disease.
Autoantibodies may be classified as (i) primary pathogenic antibodies, which directly cause a disorder by blocking a normal cellular function or by damaging tissue, or (ii) secondary antibodies, which are not pathogenic in themselves but are produced as a result of the disease. Both types may be used as diagnostic markers.
Sensitivity and specificity of autoimmune markers
The quality of a disease marker is defined by specificity and sensitivity.
High specificity is given for a marker which does only occur in this one disease, not in related diseases nor in relatives of the patient.
This is true for example for antibodies to tissue transglutaminase (tTG) with a clinical specificity for celiac disease of up to 100 %.
A marker with high sensitivity is detectable in all or most patients with a special disease.
Again tissue transglutaminase antibodies is a good example for a marker with high sensitivity: about 96 % of patients with celiac disease have a detectable titer of anti-tTG.
A disease marker can be highly specific but quite insensitive, like for example antibodies to Sm, which are found in only 10-30 % of SLE patients but almost never in other diseases. The other way round a marker can be highly sensitive, but not too specific - like antibodies to cardiolipin, which are a marker for the antiphospholipid syndrome but also are detectable in other diseases.
EliA blood tests detect autoantibodies in sera of patients suspected to suffer from autoimmune diseases. The assays are of highest quality combining exceptional specificity with highest sensitivity.