Zinc transporter 8 autoantibody testing requires age-related cut-offs
Sian Louise Grace, Angela Cooper, Angus G Jones, Timothy James McDonald, Sian Louise Grace, Angela Cooper, Angus G Jones, Timothy James McDonald
Abstract
Introduction: Zinc transporter 8 autoantibodies (ZnT8A) are biomarkers of beta cell autoimmunity in type 1 diabetes that have become more widely available to clinicians in recent years. Robust control population-defined thresholds are essential to ensure high clinical specificity in islet autoantibody testing. We aimed to determine the optimal cut-offs for ZnT8A testing.
Research design and methods: 97.5th and 99th centile cut-offs were determined using residual clinical sera from 1559 controls aged between 0 and 83 years with no history of diabetes and a hemoglobin A1c level of less than 6.0% (<42 mmol/mol). ZnT8A were measured by ELISA (RSR, Cardiff, UK) on a Dynex DS2 ELISA robot (Dynex, Preston, UK). We assessed the impact of age-related cut-offs in comparison with the manufacturer's recommended threshold in a mixed cohort of young-onset (<age 30) diabetes (UNITED study (Using pharmacogeNetics to Improve Treatment in Early-onset Diabetes), n=145).
Results: Using the manufacturer's limit of detection, 6 WHO U/mL, 16.2% of people in the control cohort had detectable levels of ZnT8A and those who had detectable ZnT8A were much more likely to be younger (p<0.0001). The 97.5th and 99th centile thresholds were substantially higher in younger participants: 18 and 127 WHO U/mL (tested under 30 years) in comparison with 9 and 21 WHO U/mL (tested 30 years and over). In the UNITED cohort some of those found to be ZnT8A-positive by the manufacturer's threshold but negative using the appropriate 99% centile cut-off (127 WHO U/mL) displayed characteristics suggestive of type 2 diabetes.
Conclusions: Age-related thresholds are needed for ZnT8A testing. In those aged <30 years, use of manufacturers' recommended cut-offs may result in low test specificity and potentially high rates of false positive test results in patients who do not have autoimmune diabetes.
Trial registration: ClinicalTrials.gov NCT01238380.
Keywords: autoantibodies; autoimmunity; biomarkers; diabetes mellitus; type 1.
Conflict of interest statement
Competing interests: None declared.
© Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.
Figures
![Figure 1](https://www.ncbi.nlm.nih.gov/pmc/articles/instance/8340275/bin/bmjdrc-2021-002296f01.jpg)
Figure 2
Plot of ZnT8A titers in…
Figure 2
Plot of ZnT8A titers in healthy controls (n=1559). Dotted lines indicate the 97.5th…
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- Research Support, Non-U.S. Gov't
- Adolescent
- Adult
- Aged
- Aged, 80 and over
- Autoantibodies
- Cation Transport Proteins* / genetics
- Child
- Child, Preschool
- Diabetes Mellitus, Type 1* / diagnosis
- Diabetes Mellitus, Type 2*
- Humans
- Infant
- Infant, Newborn
- Middle Aged
- Young Adult
- Zinc Transporter 8
- Autoantibodies
- Cation Transport Proteins
- Zinc Transporter 8
- ClinicalTrials.gov/NCT01238380
- Full Text Sources
- Medical
![Figure 2](https://www.ncbi.nlm.nih.gov/pmc/articles/instance/8340275/bin/bmjdrc-2021-002296f02.jpg)
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Source: PubMed