LEARNING OBJECTIVES
After completing Module 4, the learner should be able to:
1. Name at least two methods of screening for islet autoantibodies as well as the advantages and limitations of each method.
2. Describe at least two organizations or companies that offer islet autoantibody screening.
3. Explain why positive screening results must always be followed by confirmation testing.
Screening​ Methods
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Module Authors: Patricia Gesualdo, Kimber Simmons
Testing for Islet Autoantibodies (IAb): GADA, IAA, IA-2A, and ZnT8A
Islet autoantibodies, including insulin autoantibody (IAA), GAD autoantibody (GADA), insulinoma antigen-2 autoantibody (IA-2A), and zinc transporter type 8 autoantibody (ZnT8A), are a specific set of markers in the bloodstream that are linked to the development of type 1 diabetes (T1D). T1D-associated antibodies can be measured by clinical, direct-to-consumer, or research labs.
Islet autoantibody screening is readily available and can be easily done with a small sample of capillary or venous blood. There are several assay methods for autoantibody measurement and there is variation across labs with respect to the number/types of antibodies assayed, the methods used for testing autoantibody levels and test-specific performance characteristics.(1-3) Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) are not established for many labs. Screening tests are designed to be followed by confirmation tests to avoid raising patient anxiety with a false-positive result. In combination with metabolic testing (A1c, glucose levels), confirmed autoantibody results are required to accurately determine the stage of T1D.
ISLET AUTOANTIBODY ASSAY METHODS
Radiobinding Assay (RBA)
RBA is a method that uses radioisotopes to detect islet autoantibodies. Most historical data in type 1 diabetes literature uses the RBA method. In RBA, a radioactively labeled antigen is used to detect the binding of autoantibodies to that antigen. The amount of radioactivity is measured to determine the presence and level of autoantibodies.
Electrochemiluminescence (ECL)
ECL is a newer, radiation-free method that relies on the emission of light when a substance undergoes a chemical reaction for detection of a positive result. Detection requires the binding of two labelled antigens with the autoantibody acting as a “bridge” between the antigen which binds to the detection plate and an antigen which is labelled for detection. This signal is then quantified to determine the presence and level of autoantibodies. The ECL method is both sensitive and specific for high-affinity autoantibodies. ECL assays can be multiplexed using different labels for different autoantibodies allowing the measurement of multiple autoantibody types in a single tube.
Enzyme-linked Immunosorbent Assay (ELISA)
ELISA uses specialized enzymes that attach to antibodies in blood. These tests are less sensitive and more likely to miss those with autoantibodies.​
Antibody Detection by Agglutination-PCR (ADAP)
This assay can be performed on dried blood spot samples. Autoantibodies bind to synthetic antigen–DNA conjugates. These antibody-antigen-DNA complexes then agglutinate, enabling ligation of the DNA strands. Level of autoantibody can then be quantified by qPCR. ADAP assays can be multiplexed allowing single sample measurement of multiple islet autoantibodies.
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Indirect Fluorescent Antibody (IFA) for Islet-Cell Antibodies (ICA)
This a cell-based assay which measures the binding of the tested serum to a human islet. This assay detects autoantibodies targeting multiple antigens, in contrast to the other methods which are specific for single autoantibodies (GADA, IAA, IA-2A and ZnT8A).
Research, Consumer and Clinical Screening Options
Several screening programs designed to identify these antibodies are accessible in the United States and these programs vary in screening strategy, eligible participants and geographical areas covered (see Table 1). There are also several clinical and consumer laboratories which measure islet autoantibodies using a variety of assay types (Table 1). More information and guidance on test selection can be found on Ask the Experts website, or by emailing Questions@AsktheExperts.org OR calling 303-724-1212.
TABLE 1 Screening Programs
REFERENCES
1. Jia X, Yu L. Effective assay technologies fit for large-scale population screening of type 1 diabetes. Front Clin Diabetes Healthc 2022;3:1034698.
2. Thomas NJ, Jones AG. The challenges of identifying and studying type 1 diabetes in adults. Diabetologia 2023;66(12):2200–12.
3. Chiarelli F, Rewers M, Phillip M. Screening of Islet Autoantibodies for Children in the General Population: A Position Statement Endorsed by the European
Society for Paediatric Endocrinology. Horm Res Paediatr 2022;95(4):393–6.
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