Implementing the VA/DoD Type 2 Diabetes Mellitus Clinical Practice Guideline

Dr. Conlin. Many patients tend to be deferential to their health care providers. They were brought up in an era where they needed to listen to and respect clinicians rather than participate in discussions about their ongoing care. How do you engage with these patients?

Dr. Watts. That is a tough one. Before the patient leaves the office, I ask them: Are there any barriers? Does this work for your schedule? Is this a preference and value that you have? Is there anything that might get in the way of this working when you go home? I try to pull out a little bit more, making sure to give them some decision aids and revisit it at the next visit to make sure it’s working.

Dr. Conlin. We’ll now turn to a discussion of using hemoglobin A_1c (HbA_1c) measurements in clinical practice. Dr. Aron, what factors can impact the relationship between HbA_1c and blood glucose? How should we use HbA_1c in the treatment of patients who come from varied ethnic and racial backgrounds, where the relationship to average blood glucose may be different?

David C. Aron, MD, MS. The identification of HbA_1c has been a tremendous advance in our ability to manage patients with diabetes. It represents an average blood glucose over the preceding 3 months but like everything in this world, it has issues. One is the fact that there is a certain degree of inaccuracy in measurement, and that’s true of any measurement that you make of anything. Just as you allow a little bit of wiggle room when you’re driving down the New Jersey Turnpike and watching your speedometer, which is not 100% accurate. It says you are going 65 but it could, for example be 68 or 62. You don’t want to go too fast or you’ll get a speeding ticket. You don’t want to go too slowly or the person behind you will start honking at you. You want to be at the speed limit plus or minus. The first thing to think about in using HbA_1c is the issue of accuracy. Rather than choose a specific target number, health care providers should choose a range between this and that. There’ll be more detail on that later.

The second thing is that part of the degree to which HbA_1c represents the average blood glucose depends on a lot of factors, and some of these factors are things that we can do absolutely nothing about because we are born with them. African Americans tend to have higher HbA_1c levels than do whites for the same glucose. That difference is as much as 0.4. An HbA_1c of 6.2 in African Americans gets you a 5.8 in whites for the same average blood glucose. Similarly, Native Americans have somewhat higher HbA_1c, although not quite as high as African Americans. Hispanics and Asians do as well, so you have to take your patient’s ethnicity into account.

The second has to do with the way that HbA_1c is measured and the fact that there are many things that can affect the measurement. An HbA_1c is dependent upon the lifespan of the red blood cell, so if there are alterations in red cell lifespan or if someone has anemia, that can affect HbA_1c. Certain hemoglobin variants, for example, hemoglobin F, which is typically elevated in someone with thalassemia, migrates with some assays in the same place as thalassemia, so the assay can’t tell the difference between thalassemia and hemoglobin F. There are drugs and other conditions that can also affect HbA_1c. You should think about HbA_1c as a guide, but no number should be considered to be written in stone.

Dr. Conlin. I can imagine that this would be particularly important if you were using HbA_1c as a criterion for diagnosing diabetes.

Dr. Aron. Quite right. The effects of race and ethnicity on HbA_1c account for one of the differences between the VA/DoD guidelines and those of the American Diabetes Association (ADA).

Dr. Conlin. Isn’t < 8% HbA_1c a national performance measure that people are asked to adhere to?

Dr. Aron. Not in the VA. In fact, the only performance measure that the VA has with a target is percent of patients with HbA_1c > 9%, and we don’t want any of those or very few of them anyway. We have specifically avoided targets like < 8% HbA_1c or < 7% HbA_1c, which was prevalent some years ago, because the choice of HbA_1c is very dependent upon the needs and desires of the individual patient. The VA has had stratified targets based on life expectancy and complications going back more than 15 years.