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

Dr. Conlin. Another issue that can confuse clinicians is when the HbA_1c is in the target range but actually reflects an average of glucose levels that are at times very high and very low. How do we address this problem clinically?

Dr. Aron. In managing patients, you use whatever data you can get. The HbA_1c gives you a general indication of average blood glucose, but particularly for those patients who are on insulin, it’s not a complete substitute for measuring blood glucose at appropriate times and taking the degree of glucose variability into account. We don’t want patients getting hypoglycemic, and particularly if they’re elderly, falling, or getting into a car accident. Similarly, we don’t want people to have very high blood sugars, even for limited periods of time, because they can lead to dehydration and other symptoms as well. We use a combination of both HbA_1c and individual measures of blood glucose, like finger-stick blood sugar testing, typically.

Dr. Conlin. The VA/DoD CPG differs from other published guidelines in that we proposed patients are treated to HbA_1c target ranges, whereas most other guidelines propose upper limits or threshold values, such as the HbA_1c should be < 7% or < 8% but without lower bounds. Dr. Colburn, what are the target ranges that are recommended in the CPG? How were they determined?

Maj. Jeffrey A. Colburn, MD. It may be helpful to pull up the Determination of Average Target HbA_1c Level Over Time table (page S17), which lays out risk for patients of treatment as well as the benefits of treatment. We first look at the patient’s state of health and whether they have a major comorbidity, a physiologic age that could be high risk, or advanced physiologic age with a diminished life expectancy. In controlling the levels of glucose, we’re often trying to benefit the microvascular health of the patient, realizing also that eventually poor management over time will lead to macrovascular disease as well. The main things that we see in child data is that the benefits of tight glucose control for younger patients with shorter duration of type 2 diabetes mellitus (T2DM) is the prevention of retinopathy, nephropathy, and peripheral neuropathy. Those patients that already have advanced microvascular disease are less likely to benefit from tight control. Trying to push glucose very low can harm the patient. It’s a delicate balance between the possible benefit vs the real harm.

The major trials are the ADVANCE, ACCORD, and the VADT trial, which was done in a VA population. To generalize the results, you are looking at an intensive control, which was trying to keep the HbA_1c in general down below the 7% threshold. The patients enrolled in those trials all had microvascular and macrovascular disease and typically longer durations of diabetes at the time of the study. The studies revealed that we were not preventing macrovascular disease, heart attacks, strokes, the types of things that kill patients with diabetes. Individuals at higher HbA_1c levels that went down to better HbA_1c levels saw some improvement in the microvascular risk. Individuals already at the lower end didn’t see as much improvement. What we saw though that was surprising and concerning was that hypoglycemia, particularly severe hypoglycemia in the VADT trial was a lot more frequent when you try and target the HbA_1c on the lower end. Because of these findings, we proposed the table with a set of ranges. As Dr. Aron noted, HbA_1c is not a perfect test. It does have some variance in the number it presents. The CPG proposed to give individuals target ranges. They should be individualized based upon physiologic age, comorbidities, and life expectancy.

A criticism of the table that I commonly hear is what’s the magic crystal ball for determining somebody’s life expectancy? We don’t have one. This is a clinician’s judgment. The findings might actually change over time with the patient. A target HbA_1c range is something that should be adapted and evolve along with the clinician and patient experience of the diabetes.

There are other important studies. For example, the UKPDS trials that included patients with shorter durations of diabetes and lesser disease to try and get their HbA_1c levels on the lower end. We included that in the chart. Another concept we put forward is the idea of relative risk (RR) vs absolute risk. The RR reduction doesn’t speak to what the actual beginning risk is lowered to for a patient. The UKPDS is often cited for RR reduction of microvascular disease as 37% when an HbA_1c of 7.9% is targeted down to 7.0%. The absolute risk reduction is actually 5 with the number needed to treat to do so is 20 patients. When we present the data, we give it a fair shake. We want individuals to guide therapy that is going to be both beneficial to preventing outcomes but also not harmful to the patient. I would highly recommend clinicians and patients look at this table together when making their decisions.