Endocrine Abstracts

Introduction: Zinc transporter 8 (ZnT8) autoimmunity has been established as one of the markers for the diagnosis of type 1 diabetes (T1D) along with glutamate decarboxylase (GAD) and tyrosine phosphatase IA-2 (IA-2) antibodies. The aim of this study is to understand the status of pancreatic autoimmunity in the diagnosis of T1D, with special attention to the usefulness of ZnT8. In addition, as a second objective, we study the proposal to perform the assessment of pancreatic autoimmunity using a stepwise approach.

Methods: We studied all ZnT8 tests performed in Asturias (Spain) since the introduction of ZnT8 analysis in April 2017 until December 2020 and how many of the 304 new diagnoses of T1D in this period had ZnT8, GAD or IA2 as the only positive antibody. Autoinmunity was considered positive if GAD>10, IA2>10 and ZnT8>20 units/ml. Finally, the proposed stepwise assessment is determined with initial analysis of GAD, subsequent study of IA2 if GAD negative and final evaluation of ZnT8 if the previous two were negative.

Results: Since the introduction of ZnT8 in our laboratory, 2388 studies have been performed in a total of 2096 patients, with a duplication in 188 patients. Of these 2096 patients, 266 patients (12.69%) had anti-ZnT8. Of these, 146 were new diagnosis of T1D in this period. In the 304 patients diagnosed with T1D included, the prevalence of anti-GAD was 74.01%, anti-IA2 45.07% and anti-ZnT8 48.03%. Of these patients, 5.59% had ZnT8 as the only positive antibody, while in the case of GAD and IA2 it was 31.58% and 6.91%, respectively. Regarding the stepwise study proposal, of the 304 patients diagnosed with T1D, 225 had anti-GAD and therefore no IA-2 or ZnT8 study would be performed in them. Of the remaining 79 patients, 45 were positive for IA2 and would not need to be tested for ZnT8. Therefore, if the analysis would have been performed in a staggered manner, 74.01% of the IA2 and 88.82% of the ZnT8 studies would have been avoided.

Conclusions: The frequency of GAD is higher than IA2 and ZnT8 and may serve as the first antibody to be requested in case of suspected T1D. ZnT8 is useful in a limited number of patients so measures should be sought to increase the effectiveness of the technique. The assessment of pancreatic autoimmunity in a stepwise manner may be a useful strategy to reduce unnecessary testing and consequently reduce healthcare costs.