A proposed reference change value for an IgA anti-tissue transglutaminase immunoassay to improve interpretation of serial results in celiac patients

Celiac disease (CD) is an autoimmune disorder caused by an inappropriate immunological response to gluten ingestion in genetically susceptible individuals. IgA anti-tissue transglutaminase (tTG) antibodies have been widely employed as a specific biochemical marker for CD. Recent studies have also shown its usefulness in evaluating patient compliance with a gluten-free diet. A group of 28 subjects with CD was selected for the study. Each fulfilled the requirement of a gluten-free diet for more than one year. IgA anti-tTG determination was performed every two months for half a year. These data were used to estimate the biological variation (BV) of IgA anti-tTG in celiac patients and to calculate the reference change value (RCV). The within-subject biological variation (CVI) and between-subject biological variation (CVG) were 19.2% and 75.6%, respectively, and the index of individuality was 0.25. The RCV calculated using these data together with our analytical imprecision (5.7%) was 55.5% for a 95% level of significance. We have determined for the first time the BV and the RCV for IgA anti-tTG in a celiac population. This value and the probability curve generated from our data could be a valuable tool for monitoring patients' adherence to dietary treatment. •We estimate the biological variation for an IgA anti-tissue transglutaminase assay.•These data are used to calculate the reference change value (RCV).•Its strong individuality supports the use of RCV in monitoring serial results.•Our result could be a valuable tool for assessing adherence to gluten-free diet.