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Diabetes Standards of Care & Clinical Practice Resources

Distinguishing Between Type 1 and Type 2 Diabetes

While the vast majority of American Indian and Alaska Native (AI/AN) patients with diabetes have type 2, type 1 diabetes and its variants do occur in AI/AN patients, particularly those of mixed heritage. Type 1 diabetes must be considered in patients of any age or weight who present with a new onset of diabetes and an unclear clinical picture. This is especially true in children, even if they are overweight.

Although no test can distinguish definitively between type 1 and type 2 diabetes, several laboratory studies may be helpful when the diagnosis is not clinically clear. Providers should consider obtaining consultation if they are unfamiliar with the use of these tests or how to make a diagnosis in a complex patient.

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Distinguishing Between Type 1 and Type 2 Diabetes Sections

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Clinical Practice Recommendations

Recommendations for Distinguishing Between Type 1 and Type 2 Diabetes

  • Consider a diagnosis of type 1 diabetes or one of its variants in AI/AN patients of any age or weight who present with a new onset of diabetes and an unclear clinical picture.
  • Obtain laboratory studies and exams as needed to aid in diabetes classification.

Measurement of Endogenous Insulin Secretion

The results for tests to measure endogenous insulin secretion may be low in type 2 diabetes patients with glucose toxicity. If in doubt, measure the following after glycemic control has been restored for several weeks:

  • Fasting insulin level – if the patient is not on exogenous insulin
  • C-peptide (the other half of pro-insulin) – this is useful even if the patient is taking insulin injections.

Autoantibody Tests

Positive antibody tests denote an autoimmune process, but negative tests do not rule it out:

  • IA-2 (Insulinoma-associated protein-2)
  • GAD-65 (Glutamic acid decarboxylate-65)
  • Other antibody tests have been used in research and clinical settings – e.g., ZnT8 (Zinc Transporter 8), thyroid peroxidase antibodies, insulin autoantibodies

Other Lab Tests and Exams

Although some overweight type 1 diabetes patients may have some signs of insulin resistance, in general, they will not have the usual type 2 diabetes measurements at diagnosis. Gauging the degree of insulin deficiency versus insulin resistance with the following tests can be helpful:

  • 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 time of diabetes diagnosis.
  • Ketones – Although patients with type 2 diabetes can present with ketonuria and even diabetic ketoacidosis (DKA), generally these only occur 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.
  • Microvascular complications – Many type 2 diabetes patients already have some degree of retinopathy, microalbuminuria, or neuropathy at the time of diabetes diagnosis. This is seldom true of patients with type 1 diabetes.
  • 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.

Even taking the results of these tests into consideration, there still will be a few patients whose type of new-onset diabetes is not initially clear; over time, however, the diagnosis will become apparent. In the meantime, if there is concern that the patient may become acidotic if taken off insulin or if insulin is needed for glycemic control, insulin therapy should be continued, at least until it is established that it is no longer necessary.

As diabetes science has progressed and as more children are being diagnosed with diabetes, it has become clear that type 1 and type 2 diabetes are at either end of a continuum that includes autoimmune-mediated 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.

Making the distinction between type 1 and type 2 diabetes is important because it will dictate the immediate and long-term need for insulin treatment. For example, in patients with type 2 diabetes who also have one or more positive antibodies, there will be a shorter timeframe until insulin will be required – for glycemic control, if not for preventing ketosis. In patients with the type 1 variant known as Latent Autoimmune Diabetes of Adults (LADA), insulin may not be required initially, but over time they will progress to requiring insulin to avoid ketosis.

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National Institute of Diabetes and Digestive and Kidney Diseases