I frequently get asked, “What is the difference between type 1 and type 2 diabetes?” In the most basic form, it can be explained as follows:
• Type 1 diabetes is due to a lack of insulin production.
• Type 2 diabetes is due to insulin resistance (insulin does not work well).
This is an extremely important question because treatment can be significantly different. So, what do we look for to sort out the diagnosis?
There are signs that are clearly related to insulin resistance and the diagnosis of type 2 diabetes. These include being overweight/obese, presence of high blood pressure and high cholesterol and/or triglycerides. These conditions are part of the metabolic syndrome which is associated with insulin resistance and the development of type 2 diabetes. Although this has been called adult-onset diabetes in the past, we are now seeing this diagnosed in younger patients, even children and adolescents. Typically, the more weight you gain, the worse the insulin resistance gets and results in higher blood sugars. Losing weight can help in the setting of metabolic syndrome and type 2 diabetes. There are many patients with type 2 diabetes that require insulin, which has led to confusion with other older terminology such as insulin-dependent diabetes (previously used to indicate type 1 diabetes).
Type 1 diabetes has signs that can help make its diagnosis. Patients usually present with worsening blood sugars and weight loss, which can be attributed to the lack of insulin. This lack of insulin can lead to ketoacidosis, which is a common presentation of type 1 diabetes in the emergency room. Because of this, patients with type 1 diabetes tend to be more ill upon presentation. Although this was called juvenile-onset diabetes in the past, we are now seeing this diagnosed often in older patients. As a specialist, I often see patients that were diagnosed with type 2 diabetes elsewhere but are shown to have type 1 diabetes after further testing. Diagnosis in these cases is typically called latent autoimmune diabetes of adulthood (LADA).
So, what testing can we do if we are not certain? We can evaluate insulin production from the pancreas with a fasting C-peptide and glucose. C-peptide is linked to insulin when made in the pancreas and is a great indicator of the actual insulin production. Low levels indicate a higher likelihood of type 1 diabetes, while higher levels indicate insulin resistance and type 2 diabetes. Since type 1 diabetes is usually an autoimmune disease, we can also look for antibodies that correlate with development of the condition. There are a handful that we check, but the most common to check first is something called GAD-65 antibody. With low C-peptide and positive antibodies, the diagnosis of type 1 diabetes can be accurately made. There is a caveat here, because some patients with type 2 diabetes can have positive GAD-65 antibodies as well (but likely have higher C-peptide values). In the setting of insulin resistance, the positive GAD-65 can help indicate the rate to progression of insulin requirement in these patients.
Sound confusing? It certainly can be and is why I initially mentioned that the question is of utmost importance and the correct diagnosis needs to be made. This is because of different treatments for these conditions. Type 1 diabetes requires insulin administration, in the forms of a long-acting insulin and short-acting insulin before meals. As previously mentioned, type 2 diabetes may sometimes require insulin, but there are a number of other treatments available for the condition, some of which are much better to use than insulin, if possible. If you are uncertain about your own diagnosis, please have a specialist investigate further.