Autoantibody Tests
Positive islet and insulin antibody tests denote an autoimmune process and are usually detected in people with type 1 diabetes or those at increased risk for the condition. Negative tests, however, do not always rule out a diagnosis of type 1 diabetes. The following tests are commonly ordered as a panel:
- GAD-65 (Glutamic acid decarboxylase-65)
- IA-2 (Insulinoma-associated protein-2/tyrosine phosphatases)
- ZnT8 (Zinc transporter 8)
- IAA (insulin autoantibodies)
Note: The presence of multiple antibodies in asymptomatic individuals increases the likelihood of developing clinical type 1 diabetes.
Other Lab Tests and Exams
People with type 1 diabetes are generally diagnosed at a younger age (<35 years) and have a lower body mass index (BMI) <25 kg/m2. They typically present with unintentional weight loss, glucose levels >360 mg/dL, and have symptoms of hyperglycemia. Patients may present with diabetic ketoacidosis (DKA) requiring urgent treatment. Some patients with type 1 diabetes may be overweight or obese at diagnosis; however, they will not have the typical type 2 diabetes findings as described below.
- Lipids – Most type 2 diabetes patients have the typical low HDL/high triglyceride pattern.
- Blood pressure – Type 2 diabetes patients often have some degree of hypertension at the time of diabetes diagnosis.
- Microvascular complications – retinopathy, microalbuminuria, or neuropathy may be noted in patients with type 2 diabetes at diagnosis. This is seldom true of patients with type 1 diabetes.
Other differences include:
- Ketosis – Patients with ketosis-prone type 2 diabetes can present with DKA, generally occurring at very high glucose levels or with a serious concurrent illness or infection. More often, it is patients with type 1 diabetes who present with significant ketosis and who are more profoundly acidotic with DKA.
- Weight loss – The degree and speed of weight loss before diagnosis is usually more rapid in patients with type 1 diabetes than with type 2 diabetes.
- Hyperosmolar Hyperglycemic State (HHS) – Patients with type 2 diabetes may present with severe hyperglycemia (BS >600 mg/dL) and dehydration, precipitated by infection or cardiovascular event, usually requiring hospitalization. It is not seen in patients with type 1 diabetes.
Taking this information into consideration, there still may be situations in which the diagnosis of new-onset diabetes is not initially clear. Over time, however, the diagnosis will become apparent.
As diabetes science progresses, it is clear that type 1 and type 2 diabetes are at opposite ends of a continuum that includes insulin deficiency and insulin resistance. While providers easily recognize patients with classic type 1 or type 2 diabetes, there are a fair number of patients whose clinical presentation does not lend itself to such classification.
