From the Guidelines
The initial laboratory tests for diagnosing autoimmune type 2 diabetes include autoantibody testing, particularly glutamic acid decarboxylase antibodies (GADA), islet cell antibodies (ICA), insulin autoantibodies (IAA), and zinc transporter 8 antibodies (ZnT8A), as well as C-peptide measurement to assess residual beta cell function, accompanied by standard diabetes diagnostics such as fasting blood glucose, HbA1c, and oral glucose tolerance tests. These tests are crucial for distinguishing autoimmune diabetes from classic type 2 diabetes, which is characterized by insulin resistance rather than autoimmune destruction of beta cells 1. Autoimmune diabetes is suspected in adults who present with diabetes but don't fit the typical type 2 profile—they may be leaner, younger, have less metabolic syndrome features, or show poor response to oral medications. Early identification is crucial because these patients typically experience a more rapid decline in insulin production and require insulin therapy sooner than typical type 2 diabetes patients. The presence of these autoantibodies, particularly GADA, is a key marker for autoimmune diabetes, with studies indicating that GADA positivity is a strong predictor of the need for insulin therapy in patients with type 2 diabetes 1.
Some key points to consider in the diagnosis of autoimmune type 2 diabetes include:
- The use of autoantibody testing to identify patients with autoimmune diabetes, with GADA being the most sensitive and specific marker 1
- The importance of C-peptide measurement in assessing residual beta cell function, with lower levels suggesting autoimmune diabetes 1
- The need for standard diabetes diagnostics, including fasting blood glucose, HbA1c, and oral glucose tolerance tests, to confirm the diagnosis of diabetes and to assess the degree of glucose dysregulation 1
- The consideration of clinical features, such as age, body mass index, and presence of metabolic syndrome, in determining the likelihood of autoimmune diabetes 1
Overall, the diagnosis of autoimmune type 2 diabetes requires a comprehensive approach that incorporates both laboratory testing and clinical evaluation, with the goal of identifying patients who are at risk for rapid progression to insulin deficiency and who may benefit from early initiation of insulin therapy 1.
From the Research
Initial Laboratory Tests for Diagnosing Autoimmune Type 2 Diabetes
The initial laboratory tests for diagnosing autoimmune type 2 diabetes involve the detection of islet autoantibodies, which indicate an autoimmune etiology and can support the diagnosis of type 1 diabetes (T1D) or latent autoimmune diabetes in adults (LADA) [ 2, 3 ].
- The presence of islet autoantibodies, such as glutamic acid decarboxylase autoantibodies (GADA), insulinoma-associated-2 autoantibodies (IA-2A), insulin autoantibodies (IAA), and zinc transporter-8 autoantibodies (ZnT8A), can distinguish LADA from phenotypically type 2 diabetes [ 3 ].
- Autoantibody testing can also predict the development of T1D, and once safe and effective therapies are available to prevent T1D, islet autoantibody testing is expected to become a routine part of medical practice [ 2, 4 ].
- The determination of islet autoantibodies can greatly aid in the diagnosis and prediction of T1D, and autoantibodies to glutamic acid decarboxylase or ICA are of high diagnostic sensitivity in cases where patients initially diagnosed with type 2 diabetes show progression to insulin dependency [ 5 ].
Laboratory Tests for Type 2 Diabetes
For type 2 diabetes, laboratory tests include [ 6 ]:
- Fasting plasma glucose
- Hemoglobin A1c
- Oral glucose tolerance test
- Random plasma glucose
These tests can help diagnose type 2 diabetes and predict diabetic complications. However, the glycemic threshold for type 2 diabetes should be established by cost-effectiveness analysis [ 6 ].