Excellence in Autoimmunity
Specificity and sensitivity of autoantibodies
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 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 are also detectable in other diseases.