There are two major types of diabetes, Type 1 ("Juvenile diabetes" or "insulin-dependent diabetes mellitus") and Type 2 ("Adult onset" or "non-insulin dependent" diabetes mellitus (NIDDM). This article discusses a newer classification, Type 1.5. Type 1.5 is one of several names now applied to those who are diagnosed with diabetes as adults, but who do not immediately require insulin for treatment, are often not overweight, and have little or no resistance to insulin. When special lab tests are done, they are found to have antibodies, especially GAD65 antibodies, that attack their beta cells. This sort of diabetes is sometimes called Slow Onset Type 1 or Latent Autoimmune Diabetes in Adults (LADA).
One study performed in Bruneck, Italy [Diabetes, October 1998] found that 84% of the people diagnosed as Type 2 had insulin resistance, but the other 16% did not, suggesting these individuals had Type 1.5 diabetes. Several other studies have shown similar results as well as the presence of antibodies, especially those against glutamic acid decarboxylase (GAD), characteristic of Type 1 in this group of people diagnosed with Type 2.
Knowing your diabetes type can give you a better understanding of the changes that may occur as you age and the disease progresses. For example, if you have had insulin-resistant diabetes for several years that has become harder to control on a sulfonylurea medication and your C-peptide level (a lab test that measures insulin production) is now low, the addition of insulin will be needed. However, if your control of the diabetes is poor and your C-peptide is normal, adding another oral agent and paying closer attention to your food and exercise choices may be all that is required.
As insulin production falls, insulin becomes necessary to maintain control of the disease. One indication that people have Type 1.5 rather than Type 2 is their appearance, which is more likely though not always slender and physically fit. They often do not have other signs of Type 2 diabetes, such as the Syndrome X cluster of high TGs, low HDL or high blood pressure. Fortunately, in these early stages, diabetes treatment is not significantly different for slow-onset Type 1.5 patients than for truly insulin-resistant Type 2 patients. The only exception is that drugs designed to increase insulin sensitivity like the glitazones do not work because insulin sensitivity is normal.
Approximately 15% to 20% of people diagnosed as "Type 2" in fact have Type 1.5. They are often diagnosed as Type 2 because they are older and will initially respond to diabetes medications because they have adequate insulin production. The initial treatment may involve diet change, exercise and standard Type 2 medications.