254 Ten Times Normal Anti Tissue Transglutaminase Level Detected By ELISA, But Normal level by Chemiluminescent Assay

Introduction/Objective Celiac disease is a lifelong autoimmune condition requiring strict avoidance of gluten containing foods. Based on ESPAGHAN 2020, eligible children for no biopsy approach for celiac disease diagnosis are those with high serum IgA class antibody concentration against transglutaminase 2 values (more than 10 times the upper limit of normal) with appropriate tests and positive endomysial antibodies (EMA-IgA) in a second serum sample. Endoscopic studies are frequently performed in our country, especially in the pediatric age group. We encountered cases in which elevated anti TTG IgA level (ten times higher than normal) were reported in recent years, in whom a biopsy was taken from the bulb and duodenum and the sample was sent to our laboratory. Later, we checked the anti TTG IgA level using a chemiluminescent assay, and the level was reported as normal. Here, we discuss the matter just to mention that in some cases, ten times normal anti TTG IgA level by ELISA method maybe false and the level should be confirmed by CLIA method on a second blood sample. Methods/Case Report Between 2018 and March 2024, we encountered 6 children with elevated anti TTG IgA levels ten times normal, they all underwent upper endoscopy and biopsy. Anti TTG IgA levels were measured using ELISA in different laboratories and with different types of kits. EMA was measured on second blood sample in some of the patients and some had negative result. In all of these cases, biopsy was performed. At least four biopsy samples obtained from the bulb and distal duodenum in each patient (except patient number 4, one piece from bulb and two pieces from D2) and sample was sent to our laboratory (Roshan Azma Pathobiology Laboratory, Tehran, Iran). New Marsh grading system was used for histopathology report (2). After processing and embedding, two slides were taken from each sample and stained with Hematoxylin & Eosin. The slides were observed by a pathologist with approximately 27 years of experience in pediatric gastrointestinal pathology. In all cases, the second blood sample was analyzed using the chemiluminescence method (Liaison Instruments) (3). It is important to state that none of these children were on gluten free diet at the time of upper endoscopy and biopsy. Results/Conclusions Six patients with anti TTG IgA antibody levels more than 10 times the upper limit of normal detected. Four patients were male and the median age was 8.4 years. The demographic details are depicted in attached table. EMA was checked and in patients number 5 and 6, it was positive (other patients had negative EMA level). Two patients underwent repeat ELISA tests on a second blood sample in another laboratory and the results were the same (patients number 1 and number 5). All of the above mentioned cases had normal histology and normal anti TTG IgA levels by chemiluminescence method. In addition, we had patients with elevated anti TTG IgA with ELISA who had normal histology, but patients did not referred for assessment of anti TTG IgA level with chemiluminescent method and were not included in this study. Despite the highly elevated anti TTG IgA levels detected by ELISA, these cases were regarded as false positive and no gluten free diet was administered. Seven other patients had anti TTG IgA levels between 5 and 10 times normal. All patients had normal histology. The second blood sample was checked by the chemiluminescent method and the level was reported as normal.