From the Guidelines
The diagnostic tests for Diabetes Mellitus type 1 (DM1) include fasting plasma glucose, 2-h plasma glucose during a 75-g oral glucose tolerance test (OGTT), and A1C criteria, with the choice of test depending on the individual's clinical presentation and risk factors 1. The diagnosis of DM1 is typically made based on a combination of clinical presentation, laboratory tests, and autoimmune markers.
- Fasting plasma glucose equal to or exceeding 126 mg/dL (7.0 mmol/L) is considered diagnostic for DM1, as is a 2-h plasma glucose measurement at 2 hours postload equal to or exceeding 200 mg/dL (11.1 mmol/L) during an OGTT 1.
- A1C criteria can also be used to diagnose DM1, with a value of 6.5% or higher considered diagnostic 1.
- Autoimmune markers, such as 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 also be used to support a diagnosis of DM1 1. It is essential to note that the tests do not necessarily detect diabetes in the same individuals, and the efficacy of interventions for primary prevention of type 2 diabetes has primarily been demonstrated among individuals who have impaired glucose tolerance (IGT) with or without elevated fasting glucose, not for individuals with isolated impaired fasting glucose (IFG) or for those with prediabetes defined by A1C criteria 1. In conditions associated with increased red blood cell turnover, such as sickle cell disease, pregnancy (second and third trimesters), hemodialysis, recent blood loss or transfusion, or erythropoietin therapy, only plasma blood glucose criteria should be used to diagnose diabetes 1.
From the Research
Diagnostic Tests for Diabetes Mellitus Type 1
The diagnostic tests for Diabetes Mellitus type 1 (DM1) include:
- Fasting plasma glucose (FPG) levels, with a diagnostic cutoff of 126 mg/dL (7.0 mmol/L) 2, 3, 4, 5
- 2-hour plasma glucose level of 200 mg/dL (11.1 mmol/L) or more during an oral glucose tolerance test (OGTT) 2, 3, 5
- Random plasma glucose level of 200 mg/dL (11.1 mmol/L) or more 2, 3, 5
- Hemoglobin A1c (HbA1c) level of 6.5% or greater, although this test may not be suitable for all patients and should be used in combination with plasma glucose determinations 6, 5
Additional Considerations
- The American Diabetes Association recommends screening for type 2 diabetes annually in patients 45 years and older, or in patients younger than 45 years with major risk factors 5
- Screening for type 1 diabetes is not recommended 5
- A single random plasma glucose level of 200 mg/dL or greater with typical signs and symptoms of hyperglycemia likely indicates diabetes, but results should be confirmed with repeat testing on a subsequent day 5
- Additional testing to determine the etiology of diabetes is not routinely recommended 5