From the Guidelines
Type 1 Diabetes Mellitus (T1DM) diagnosis is primarily based on clinical presentation, and laboratory tests such as C-peptide measurements and autoimmune markers, including islet cell autoantibodies, can help distinguish it from Type 2 diabetes.
Laboratory Tests for T1DM
- C-peptide measurements: can help distinguish Type 1 from Type 2 diabetes in ambiguous cases, such as individuals who have a Type 2 phenotype but present in ketoacidosis 1
- Autoimmune markers: including islet cell autoantibodies, autoantibodies to insulin, autoantibodies to GAD (GAD65), autoantibodies to the tyrosine phosphatases IA-2 and IA-2b, and autoantibodies to zinc transporter 8 (ZnT8), can identify individuals at risk for developing T1DM 1
Screening for T1DM
- High-risk populations: measurement of islet autoantibodies may be appropriate in high-risk populations, such as those with prior transient hyperglycemia or those who have relatives with T1DM 1
- Asymptomatic low-risk individuals: widespread clinical testing is not currently recommended, as it would identify very few individuals in the general population who are at risk 1
Important Considerations
- Clinical presentation: T1DM is often diagnosed soon after the onset of hyperglycemia, and most cases present with acute symptoms of diabetes and markedly elevated blood glucose levels 1
- Standardization of insulin and C-peptide assays: is necessary to facilitate measures of insulin secretion and sensitivity that will be comparable across research studies 1
From the Research
Laboratory Tests for Type 1 Diabetes Mellitus (T1DM)
- The diagnosis of T1DM can be substantiated by quantifying venous plasma glucose, which is the gold standard in diagnostics 2.
- Additional tests such as HbA1c and OGTT are recommended as a precaution 2.
- Autoantibodies, including glutamic acid decarboxylase antibody (GADA), insulinoma antigen 2 antibody (IA-2A), islet cell antibody (ICA), zinc transporter 8 autoantibody (ZnT8-A), and insulin antibody (IAA), are biomarkers of T1DM-associated autoimmunity and can be used to identify individuals at risk of developing T1DM 3, 4.
- A multiplexed Array-ELISA assay can detect multiple autoantibodies simultaneously and has shown improved diagnosis accuracy compared to single target immunoblotting tests 4.
- Serum biomarkers, including glucose, glycated molecules, C-peptide, and autoantibodies, have been established for the diagnosis of T1D, but novel biomarkers are being discovered using "-omics" technologies to predict T1D development or progression 5.
- In patients with a vague clinical picture, findings of uric ketones, BGA, IA-2- and GAD-antibodies, and optionally C-peptide can help ensure diagnosis 2.
- Multiple islet-associated autoantibodies, such as GAD and IA-2 antibodies, can be present in individuals with T1DM, including elderly individuals with first-onset T1DM 6.