Cases illustrating blood glucose monitoring in type 2 diabetes

INTRODUCTION — The following cases illustrate the value of blood glucose monitoring in adults with type 2 diabetes, depending upon the time, treatment, and stage of the disease. The optimal frequency of monitoring, glucose meters and glucose test strips, and the role of continuous glucose monitoring (CGM) systems are discussed in more detail elsewhere. (See "Glucose monitoring in the ambulatory management of nonpregnant adults with diabetes mellitus".)

CASE 1 — A 56-year-old woman who is a clothing sales assistant presents with thirst, fatigue, and a vaginal yeast infection. She is 5 feet, 4 inches (163 cm) tall and weighs 265 lbs (120 kg), for a body mass index (BMI) of 45 kg/m². A random blood glucose value is 290 mg/dL (16.1 mmol/L), her glycated hemoglobin (A1C) value is 9.4 percent, and her renal and liver function are normal. She eats a diet high in fat and refined carbohydrate, and she exercises little. She watches television for several hours nearly every evening, during which time she often eats two or three sugar-covered donuts. She does not have a history of cardiovascular disease, but she has had frequent urinary tract infections. She is willing to make lifestyle changes and is reluctant to take too many medications.

Initial treatment — Appropriate initial management includes the following (see "Initial management of hyperglycemia in adults with type 2 diabetes mellitus"):

●Diabetes education in the form of written material, videos, and, if available, meeting with a diabetes educator, attending diabetes self-management training classes, and/or through a support group with other individuals with type 2 diabetes and obesity.

●Lifestyle modification, such as reducing caloric intake, eliminating refined carbohydrate, and beginning an exercise program. She may start with walking 10 to 15 minutes daily and gradually increase the walking to reach her goal (30 minutes daily at least five days or evenings a week).

●Initiation of metformin, increasing the dose gradually to 2 grams daily in divided doses.

●Blood glucose monitoring, initially every morning (fasting) and occasionally two to three hours after eating and before and after exercise. Daily fasting blood glucose values and periodic postprandial glucose monitoring will provide her with immediate feedback about the consequences of her behaviors. Her goal is to have fasting and premeal glucose readings of 80 to 130 mg/dL (4.4 to 7.2 mmol/L) and two- to three-hour postprandial glucoses of <180 mg/dL (10.0 mmol/L).

If she was catabolic on presentation with symptoms of hyperglycemia and unintentional weight loss, A1C >10 percent (86 mmol/mol), or glucose readings >300 mg/dL (16.7 mmol/L), insulin therapy is often indicated, starting with basal insulin therapy and adding prandial insulin if needed. In this setting, blood glucose monitoring before and after meals would help with dietary decisions as well as with adjusting the insulin therapy. With successful lifestyle change, weight loss, and reduction/elimination of the glucotoxicity, it may be possible to transition the patient from insulin to non-insulin therapies. However, some people with type 2 diabetes have more severe insulin deficiency and require ongoing insulin therapy.

Initial follow-up — She has been taking metformin 1000 mg twice daily, which has been well tolerated. She notes that her glucose levels rise after breakfast as well as after dinner, with considerable variability after these meals. The glucose levels do not rise after lunch since she began eating a large salad for lunch. She notes that glucose levels are higher after eating pancakes with syrup and drinking orange juice and are lower after eating eggs with one slice of whole wheat toast for breakfast. They are highest after eating pasta or pizza for dinner.

She keeps a food diary and meets with a registered dietitian, learning about the carbohydrate and caloric content of foods and portion sizes. She starts using a phone app that helps her keep track of the carbohydrates and calories in each meal, as well as of her daily steps, which help her reduce her glycemic variability and lose weight. Her thirst, fatigue, and vaginal infection subside soon thereafter.

●After two months, her fasting blood glucose values during a typical week range from 141 mg/dL (7.8 mmol/L) to 204 mg/dL (11.3 mmol/L) as shown in the table (table 1).

●After three months, she has increased her exercise program to 30 minutes five evenings per week, and she continues to eat a very low carbohydrate lunch (mostly salads). Her weight falls to 238 lbs (108 kg), her mean fasting blood glucose concentration is 178 mg/dL (9.9 mmol/L), and her A1C value is 8.3 percent.

You suggest use of a real-time continuous glucose monitor (CGM) for one week. After reviewing the CGM data, she is surprised to see large rises in her glucose concentrations after breakfast and dinner (figure 1). This further motivates her to reduce her carbohydrate intake for those meals.

She has learned a lot about diabetes and its possible future consequences from her reading and support group meetings, and she has made her short-term goal an A1C value below 7.5 percent, and her longer-term goal an A1C below 7.0 percent.

Subsequent treatment — She is congratulated on the good lifestyle choices she is making and is encouraged to continue with these. In order to meet her A1C goal, she is also given several additional pharmacologic options. Given her desire to continue to lose weight, a once-weekly glucagon-like peptide 1 (GLP-1) receptor agonist is added to metformin. This class of drugs aids with weight loss. She is asked to continue to measure her blood glucose every morning before breakfast and occasionally at other times. (See "Glucagon-like peptide 1-based therapies for the treatment of type 2 diabetes mellitus", section on 'Weight loss'.)

Sodium-glucose co-transporter 2 (SGLT2) inhibitors can also help with weight loss and would be preferred in the presence of heart failure. However, she has a history of recurrent urinary tract infections, and there is increased risk of developing these infections while taking SGLT2 inhibitors. If cost was a major issue, she could add a sulfonylurea drug instead of the GLP-1 receptor agonist, understanding that weight gain and hypoglycemia are potential side effects. Because thiazolidinediones are associated with weight gain, they are not recommended for her. Dipeptidyl peptidase 4 (DPP-4) inhibitors are weight neutral, but are expensive and, in general, not as efficacious as the GLP-1 receptor agonists. (See "Management of persistent hyperglycemia in type 2 diabetes mellitus", section on 'Monotherapy failure'.)

During the next three months, her blood glucose readings continue to improve, she continues to lose weight, and her A1C is now 7.3 percent. She is congratulated on her progress and is encouraged to continue her weight management program and the metformin. The dose of the GLP-1 receptor agonist is increased to the maximum dose. With continued weight loss and a higher dose of the GLP-1 receptor agonist, she should be able to reach her A1C goal (less than 7 percent).

If an individual cannot reach their A1C goal with metformin and a GLP-1 receptor agonist, an additional oral glucose-lowering medication can be added. When combination non-insulin therapy is insufficient, insulin therapy should be initiated, usually starting with the addition of a once-daily basal insulin. (See "Management of persistent hyperglycemia in type 2 diabetes mellitus", section on 'Dual agent failure' and "Insulin therapy in type 2 diabetes mellitus", section on 'Designing an insulin regimen'.)

It should also be emphasized that one of the most common reasons for having an A1C that is too high is "clinical inertia" where additional treatments in a stepped protocol are not added soon enough.

CASE 2 — A 63-year-old man with obesity has had diabetes for 33 years. His diabetes is complicated by nephropathy, neuropathy, hypertension, foot ulcer, proliferative diabetic retinopathy, and peripheral arterial disease. He is followed in a wound clinic for his foot ulcer and was told to avoid weight bearing until it has healed. His diabetes medications include:

●Metformin 1000 mg twice daily

●Semaglutide 1 mg weekly

●Insulin glargine 26 units at bedtime, and insulin aspart with meals

He mostly forgets to take the aspart with meals, and he snacks throughout the day, especially in the afternoon and evening. He checks his blood glucose fasting, and his mean fasting glucose is 148 mg/dL (8.2 mmol/L) with rare mild hypoglycemia. His A1C is 8.2 percent.

Interpretation and approach — The dose of semaglutide was increased to 2 mg weekly. In addition, his diabetes provider recommends that he use an intermittent scanning continuous glucose monitor (CGM) to determine the extent of within-day and between-day variations in blood glucose. Intermittent scanning CGM devices (also called flash CGM) are less expensive than real-time CGM devices. As with real-time CGM devices, the glucose sensor is placed subcutaneously. To view recent glucose readings and trend arrows, the user swipes a reader or smartphone over the sensor/transmitter, which is worn on the arm. Only the last eight hours of individual glucose readings are reported on the device or smartphone graph (ambulatory glucose profile).

The two-week summary data were downloaded at his follow-up visit (figure 2). He was surprised to see persistently elevated glucose readings related to meal-time eating and snacking. He started to pay more attention to his food (especially carbohydrate) intake and to take insulin aspart with meals using an insulin-to-carbohydrate ratio. He also reduced his evening snacking. A morning dose of insulin glargine was added and his evening insulin glargine dose reduced. With these changes, his glycemic control improved, and his foot ulcer healed.

OVERALL COMMENTS — In these cases, we are trying to show how testing blood glucose at different times of the day and in different situations can facilitate lifestyle changes and direct pharmacologic therapy. Real-time and intermittent scanning continuous glucose monitoring (CGM) devices can provide important information with which some motivated people can modify their behavior. The use of a professional CGM, which is worn for a short period of time and then returned to the clinic for interpretation, can also be instructive. CGM will be effective only if the person is able to use the information to make appropriate dietary or therapeutic adjustments. There are fewer trials evaluating the benefit of CGM in people with type 2 than type 1 diabetes. The use of such technology should be individualized depending on individual preference and motivation to make lifestyle changes. (See "Glucose monitoring in the ambulatory management of nonpregnant adults with diabetes mellitus", section on 'Type 2 diabetes'.)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Type 2 diabetes (The Basics)")

●Beyond the Basics topics (see "Patient education: Type 2 diabetes: Overview (Beyond the Basics)" and "Patient education: Glucose monitoring in diabetes (Beyond the Basics)")

ACKNOWLEDGMENT — The editorial staff at UpToDate acknowledge David McCulloch, MD, who contributed to earlier versions of this topic review.