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 or LADA.
About 15% to 20% of people diagnosed as "Type 2" actually have this type. 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 treatment the person is first put on may be diet, exercise, and standard Type 2 medications.
Since insulin resistance is minimal or non-existent, medications designed to reduce insulin resistance such as Avandia and Actos are not effective. Other meds that stimulate the pancreas to produce insulin, slow digestion of carbs, or reduce excess glucose production by the liver are often effective in controlling the blood sugar for a few years.
One study done in Bruneck, Italy, published in the October, 1998, issue of Diabetes, 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. Several other studies have shown similar results, and these studies also often show the presence of antibodies, especially those against glutamic acid decarboxylase or GAD, characteristic of Type 1 in this group of people diagnosed with Type 2.
A misdiagnosis is easy to make when the person is older and responds well at first to treatment with oral medications. If someone does not clearly fit the model for Type 1, they may be mistakenly placed on oral agents even though limited capacity for insulin production remains. The immune system's slower and more selective attack on the beta cells allows these cells to function to a high degree for a few years. On average, insulin is required in half of those with Type 1.5 diabetes within four years of diagnosis, compared to over ten years in those with true Type 2 (Endocrine Practice, v7 n5, Sept/Oct 2001, pgs 339-345).
Knowing your diabetes type can give you a better understanding of the changes that may occur to you as you age and your 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. But if your control 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's needed.
In the late 1990's, Dr. David Bell, a clinician and researcher in Birmingham, Alabama, wanted to see if he could eliminate insulin use in a group of people with Type 2 diabetes who were already on insulin by using a combination of oral medications. These people often had been put on insulin without first trying oral medications because today's array of medications were not available when they were diagnosed.
Dr. Bell first tested C-peptide levels and chose only those who had normal levels. Of the 130 people with adequate C-peptide levels in his study, 100 were able to discontinue insulin use altogether and control their diabetes on various doses of glyburide and metformin. He found that their overall control, measured by their HbA1c levels, was actually better on two oral medications than it had been previously on two daily doses of insulin. Others in the study were able to improve their hemoglobin levels by using glyburide and metformin with a single dose of insulin at dinner or bedtime.
Researchers have determined that the Type 2 patients most likely to control their blood sugars on combination oral agents are those least overweight (BMI of 30 or less), with shortest duration of diabetes, and C-peptide levels normal or only slightly low.
As insulin production falls, insulin becomes necessary to maintain control. One clue 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. Luckily, in these early stages, diabetes treatment is not significantly different for slow-onset Type 1s compared to truly insulin-resistant Type 2s. The only exception is that drugs designed to increase insulin sensitivity like the glitazones do not work because insulin sensitivity is normal.
One major benefit to this type is that when their blood sugars are controlled, people with Type 1.5 usually do not have the high risk for heart problems more often found with the high cholesterol and blood pressure seen in true Type 2 diabetes.