The “Wrong Call”: Mistaking Type 2 for Type 1

Many have asked me about this week about the recent article in the WSJ that was generated from a recent piece that pointed out how type 1 diabetes can sometimes be missed when an adult is thought to have type 2 diabetes. This is nothing new, sadly, but the rising incidence of type 1 as well as type 2 diabetes makes this a critical point to reconsider. Mistaking Type 2 for Type 1 is a potentially fatal error.

At Kovler, we know there in fact many kinds of diabetes and at least some of them can be seen at any age. As the WSJ article correctly points out, Type 1 diabetes use to be to thought of as occurring primarily in children, but this was always a misconception. While the peak ages for type 1 diabetes occur in the childhood to adolescent age group, I have had adult patients as old as 80 years of age receive a new diagnosis Type 1.

The first thing (but not the only thing!) to consider is the BMI (body mass index). Lean patients are much more likely to have type 1 diabetes or some other form of insulin-deficient diabetes (like monogenic, see below).  If the blood sugar is over 250 mg/dl it is very important to consider getting ketone levels. A positive test for acetone or other ketones is not definitive for type 1 but it should raise suspicions when the blood sugar is high.  Adults with type 1 often have a much slower time of progression of their disease, which can also be confusing. Children can appear to develop diabetes practically overnight requiring insulin right away, whereas adults with type 1 might take several years of progressive failure of one oral agent after another until insulin is finally started. This is also known as LADA – latent adult onset diabetes with autoimmunity. The autoimmunity part is really critical. Most but not all patients with type 1 will be positive for auto-antibodies against proteins of the beta cell. Typically we test for anti-GAD65, anti-IA2, anti-insulin, anti-ICA, and/or antiZnT8 antibodies. A positive test in any one of these is consistent with autoimmune type 1 diabetes, and insulin is the only appropriate therapy, although combinations that include insulin can often be helpful. The family history can also provide important  insights. Patients with type 2 diabetes actually have a positive family history of type 2 diabetes much often than patients with type 1 diabetes. Finally in some cases measuring the insulin levels can be helpful if they are high or very low. This is usually done by measuring the c-peptide level, a by-product of insulin secretion that was discovered at the University of Chicago. There are many caveats to this test so by itself it might be misleading in a non-research setting.

I should point out that there are other important forms of diabetes. Most primary care providers would be familiar with steroid-induced diabetes and gestational diabetes. While steroid-induced is a form of Type 2, gestational could be either type 1 or type 2 or monogenic and should be investigated further. Diabetes can also be associated with acromegaly, thyroid disease, and cystic fibrosis, for example.

Our team studies rare forms of diabetes that are strongly inherited – the monogenic forms. These are described on our website www.monogenicdiabetes.org, and several of them were also discovered here at the University of Chicago. These also have the hallmarks of young onset, are antibody negative, and usually positive for tests of insulin production such as the c-peptide test. They are important because they can have specific outcomes, specific treatments, and specific associated factors. They also tell us about genes that are important for normal metabolism. They occur in about 2% of everyone with diabetes, meaning about 3-500,000 people in the United States alone have one of these forms – a significant number that is largely missed.

The bottom line here is that Type 1 diabetes is increasing  in many populations, although perhaps not as dramatically as Type 2 diabetes associated with obesity. Missing type 1 diabetes can be a disaster, or at best a multiyear confusion. What I teach is that it is always important to ask oneself why a given patient has diabetes and what kind they have. Do not assume. If you have doubts, get another opinion, or get a referral to a see a specialist. Persistence can be life-saving.

Lou Philipson

Louis Philipson, M.D., Ph.D., FACP
Professor
Departments of Medicine and Pediatrics- Section of Endocrinology, Diabetes and Metabolism
Director, Kovler Diabetes Center