From the Guidelines
To confirm whether a young adult with unmanaged diabetes has type 1 or type 2 diabetes, measuring autoantibodies associated with type 1 diabetes, such as glutamic acid decarboxylase (GAD) antibodies, islet cell antibodies (ICA), insulin autoantibodies (IAA), and zinc transporter 8 (ZnT8) antibodies, is the most definitive approach, as recommended by the most recent study 1.
Diagnostic Approach
The diagnosis of type 1 vs type 2 diabetes in a young adult with many years of no medical contact and unmanaged diabetes requires a comprehensive approach.
- Measuring autoantibodies associated with type 1 diabetes is crucial, as the presence of one or more of these autoantibodies defines type 1 diabetes 1.
- A C-peptide test should also be ordered to assess the body's insulin production; low or undetectable levels suggest type 1 diabetes while normal or high levels point toward type 2.
- Checking HbA1c will determine overall glycemic control, with levels above 6.5% confirming diabetes.
Treatment Approach
In the interim, the patient should be treated with insulin therapy regardless of type determination, typically starting with basal insulin (like glargine or detemir) at 0.2-0.3 units/kg/day, plus mealtime rapid-acting insulin (like lispro or aspart) at 0.1-0.15 units/kg/meal, as this approach is necessary because untreated type 1 diabetes can quickly lead to diabetic ketoacidosis, a life-threatening condition 1.
Importance of Distinction
The distinction between type 1 and type 2 diabetes matters for long-term management, as type 1 patients require lifelong insulin therapy, while type 2 patients might eventually manage with oral medications, lifestyle changes, and possibly less intensive insulin regimens.
Recent Guidelines
Recent guidelines from the American Diabetes Association, as outlined in the 2025 standards of care in diabetes, emphasize the importance of risk-based screening for type 2 diabetes and prediabetes in youth, and recommend testing for diabetes-associated autoantibodies to exclude the possibility of autoimmune type 1 diabetes in children and adolescents with overweight or obesity 1.
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Testing for Confirmation of Type 1 vs Type 2 Diabetes
To confirm whether a young adult with many years of no medical contact and unmanaged diabetes has type 1 or type 2 diabetes, several tests can be performed:
- Autoantibody tests: These tests check for the presence of autoantibodies against insulin, GAD, or IA-2, which are commonly found in people with type 1 diabetes 2, 3.
- C-peptide test: This test measures the level of C-peptide in the blood, which can help distinguish between type 1 and type 2 diabetes. People with type 1 diabetes typically have low or undetectable levels of C-peptide 2, 3.
- Genetic testing: This test can identify genetic markers associated with an increased risk of developing type 1 diabetes 2, 3.
- Clinical presentation: A thorough medical history and physical examination can provide clues about the type of diabetes. For example, people with type 1 diabetes often present with rapid onset of symptoms, such as polyuria, polydipsia, and weight loss, whereas those with type 2 diabetes may have a more gradual onset of symptoms 2, 3.
Insulin Therapy
Insulin therapy can be used to manage both type 1 and type 2 diabetes:
- Rapid-acting insulin analogues, such as insulin aspart and insulin lispro, can be used to control postprandial glucose levels 4, 2, 5, 6.
- Basal insulin analogues, such as insulin glargine and insulin detemir, can be used to provide basal insulin coverage and reduce the risk of hypoglycemia 4, 2, 5, 6, 3.
- Ultra-long-acting insulin analogues, such as insulin degludec, can provide a flat and stable glucose-lowering profile with less inter-patient variation in glucose-lowering effect than insulin glargine 6.
Diagnosis and Management
A comprehensive diagnosis and management plan should be developed in consultation with a healthcare professional:
- A thorough medical history and physical examination should be performed to determine the type of diabetes and any related complications 2, 3.
- Laboratory tests, such as autoantibody tests and C-peptide tests, should be performed to confirm the diagnosis and guide treatment decisions 2, 3.
- An individualized treatment plan should be developed, taking into account the person's lifestyle, dietary habits, and medical history 2, 3.