A 2013 retrospective study of 2477 symptomatic adults (older than 18 years) who received diagnostic testing for celiac disease at 2 academic institutions in Cleveland, Ohio, evaluated the predictive value of IgA anti-tTG and EMA. Of the patients, 610 (25%) had abnormal serologic tests, and 240 (39%) underwent endoscopy with biopsy.
A total of 50 patients (21%) had biopsy results consistent with celiac disease, defined as a Marsh 3 lesion or greater.3 An IgA anti-tTG level of 118 U/mL (5.9-fold the upper limit of normal on the test) had a positive predictive value of 86.4% with a false-positive value of 2%. An EMA titer greater than 1:160 when IgA anti-tTG was between 21 and 118 U/mL had a positive predictive value of 83%.
Antibody levels 10 times normal show 100% positive predictive value
A 2008 retrospective study of one manufacturer’s IgA anti-tTG serologic test sought to establish the serologic antibody level at which the positive predictive value was 100%.4 Overall, 148 people, 15 years and older, with a positive IgA anti-tTG before biopsy or within 21 days of biopsy were included.
Of the patients biopsied, 139 (93%) had positive biopsies of Marsh 2 or greater and were diagnosed with celiac disease. Using a cut-off of 3.3 and 6.7 times the upper limit of normal, investigators calculated a positive predictive value of 95% and 98%, respectively.
A cut-off of 10 times the upper limit of normal or greater had a positive predictive value of 100%. The highest level of IgA anti-tTG in a patient who didn’t have celiac disease on biopsy was 7.3 times the upper limit of normal.