Example: coeliac disease (CD)
Coeliac disease is characterized by a lifelong intolerance to gluten from wheat, barley or rye. The overall prevalence of CD in the general population is approximately 1%. However, there are many non-diagnosed patients because about two thirds of patients do not show the typical gastrointestinal symptoms and have so-called silent or latent CD.
In contrast to other autoimmune diseases, coeliac disease has the advantage of having very sensitive and specific serological markers. A simple blood test can virtually rule out or confirm coeliac disease with almost 100% certainty. A positive screen test result usually leads to a confirmatory biopsy. This invasive diagnostic method is unpleasant, may be painful and is expensive. Unnecessary biopsies should be avoided whenever possible, and particularly in children.
High specificity of the screen tests for coeliac disease is therefore particularly important. Due to the prevalence of CD being only about 1% in a screening population, most suspected cases will prove not to have coeliac disease. Even a slight decrease in specificity will therefore dramatically increase unnecessary intestinal biopsies.
Example: 1000 schoolchildren are screened using a serological test for coeliac disease, the anti-tissue transglutaminase (tTG) test. An anti-tTG test with a specificity of 97% finds 3% = 30 children false-positive. A specificity of 99.4% (reported for Phadia's (now Thermo Fisher Scientific) anti-tTG test Celikey) finds 6 children false-positive. A specificity decrease of 2.4% results in five times more biopsies of non-coeliac children, most of which could be avoided by using the assay with the higher specificity.
All Phadia, now Thermo Fisher Scientific, autoimmunity tests are designed for the highest specificity, and are therefore the most valuable aid for clinicians in diagnostic decisions.