We actually got this on the sample submission guidelines for celiac testing from a different lab, to which we were submitting samples for something else (instructions in the same booklet). The instruction book had this info in it. The lab results from the celiac testing (at another lab, submitted by our doctor) did not say anything about this.
Did you know that steroid use, even topical use a month prior, can cause false negatives on celiac testing?
"Immunosuppressive drugs such as oral or intranasal corticosteroids (prednisone, beclomethasone, fluticasone, triamcinolone), and topical cortisone suspensions and creams, may affect test results for antibody assessment. The suggested time period to abstain from these is 4 weeks."