Hosted by Ray Shields, MD

Distinguishing type 1 diabetes and type 2 diabetes is not always straightforward, yet the distinction can be critical.  Type 1 diabetes exists in AI/AN patients and must be considered in patients of any age or weight who present with a new diagnosis of diabetes and an unclear clinical picture.  This is especially true in children, even if they are overweight.  Some type 1 variants, such as Latent Autoimmune Diabetes of Adults (LADA), may not require insulin to avoid ketosis in the early stages.  

Although no test can definitively distinguish type 1 from type 2, several laboratory studies may be helpful when the diagnosis is not clear clinically.  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.  Incorrectly diagnosing type 2 diabetes in a patient who truly has type 1 can cause considerable problems.

Measurement of endogenous insulin secretion

The results for these tests may be low in type 2 patients with glucose toxicity.  If in doubt, measure 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 test is useful even if the patient is taking insulin injections.

Autoantibodies

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

·        Islet cell antibodies (ICA)

·        Glutamic acid decarboxylate antibodies (GADA)

·        Other antibody tests have been used in research and some clinical settings (e.g. thyroid peroxidase antibodies, insulin autoantibodies, etc).

Other lab tests and exams

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

·        Lipids:  Type 2 diabetes patients have the typical low HDL/high triglyceride pattern.

·        Blood pressure:  Type 2 patients often have some degree of hypertension at diabetes diagnosis.

·        Ketones:  Although patients with type 2 can have 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 who have significant ketonuria and who are more profoundly acidotic with DKA.

·        Microvascular complications:   Many type 2 patients already have retinopathy, microproteinuria, or neuropathy at the time of diagnosis, whereas this is almost never 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 than type 2 diabetes.