Type one-and-a-half diabetes   (March 8, 2009)

For years, we have had terminology dividing diabetes into subgroups: there's "type 1" and "type 2" diabetes (type 1 is autoimmune diabetes with positive antibodies, typically showing up in children or teenagers, previously called IDDM or childhood-onset diabetes) (type 2 is insulin-resistant diabetes showing up in obese adults, whose antibody tests are negative, previously called NIDDM or adult-onset diabetes). There are other subgroups, but somehow these other varieties of diabetes didn't get their own numbers when the naming conventions were invented: there's "gestational diabetes" (diabetes first diagnosed during pregancy) and "secondary diabetes" (diabetes due to some other condition, such as thyroid disorders).

And there's another another type of diabetes, sometimes called LADA, that doesn't fit cleanly into either the type 1 or type 2 categories. People with LADA are diagnosed with what initially appears to be type 2 diabetes, and then rapidly progress to insulin-dependency. If diabetes antibodies (including "islet cell antibodies" and "GAD antibodies") are measured, they're positive, which is usually considered a hallmark of type 1 diabetes. LADA has sometimes been called type 1.5 diabetes (usually pronounced "type 1-and-a-half diabetes").

A few years ago (2003), an editorial in Diabetes Care discussed the name problem in an essay titled What's in a Name: Latent autoimmune diabetes of adults, type 1.5, adult-onset, and type 1 diabetes. The authors pointed out that patients with LADA have also been named type 1.5 diabetes, "slowly progressive type 1 diabetes," "latent type 1 diabetes," "youth-onset diabetes of maturity," and even LADA-type 1 and LADA-type 2. Another term that the authors didn't mention, but has sometimes been used, is "double diabetes."

In publications and in protocols for clinical trials, endocrinologists call the condition "LADA", although as jargon, both physicians and patients may call it "type 1.5". I'll use the two terms interchangeably.

Interestingly, neither the names LADA nor type 1.5 diabetes (nor any other!) have become an official part of the diagnostic lingo that physicians use to code for insurance reimbursement; the disorder probably fits best into the ICD-9 category 250.00, "Diabetes mellitus without complication type ii or unspecified type not stated as uncontrolled", rather than category 250.01, "Diabetes mellitus without complication type i not stated as uncontrolled".

What does all this mean for the average patient with diabetes? Well, first of all, if you were diagnosed with diabetes as an adult, you may assume you have type 2 diabetes, and not be aware that you have type 1.5 instead. If your diabetes was diagnosed after you became an adult, you probably didn't have antibody testing done. And if you were started on diet and exercise and your BG and A1C levels weren't controlled, you probably were started on pills, and if your BG and A1C deteriorated over time, insulin might eventually be added years after the diagnosis was first made. That's the usual scenario for people with type 2 diabetes.

Now, let's take the same general scenario as I described in the prior paragraph, but modify it so BG and A1C control can't be maintained, and insulin needs to be added within a year of diagnosis to control the hyperglycemia: that's typical of what's seen with LADA/type 1.5 diabetes. And if somewhere along the line your physician is astute enough to consider the possibility of LADA/type 1.5, and orders diabetes antibody testing, and the results are positive, the diagnosis is made.

There are a number of experts who feel that as soon as LADA is diagnosed, the patient should be on insulin therapy. This is based on the logic that the diabetes will prove impossible to control on diet, exercise, and oral medications, and hence might as well "bite the bullet" and start insulin immediately.

One might also make the suggestion that all people diagnosed with apparent type 2 diabetes should have antibody testing to see if they might instead be LADA diabetes. That suggestion hasn't been routinely implemented in the past, probably because of the twin demons of added cost and unreliability of the antibody assays, but doing antibody testing would seem reasonable if the patient's hyperglycemia fails to respond to the usual treatment program, or if there are atypical features about the patient's initial presentation.

Getting back to you, the patient: if you have apparent type 2 diabetes, but your BG and A1C remain high, ask to get diabetes antibody testing done. Or if you were just diagnosed with type 2 diabetes, and you don't fit the usual picture, ask for diabetes antibody testing. In either case, if you have one or more diabetes antibodies present, you have LADA. Or if you prefer, type 1.5. And start insulin therapy; you'll need it sooner, so might as well get started.