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Glucose monitoring in the ambulatory management of nonpregnant adults with diabetes mellitus

Glucose monitoring in the ambulatory management of nonpregnant adults with diabetes mellitus
Author:
Ruth S Weinstock, MD, PhD
Section Editor:
Irl B Hirsch, MD
Deputy Editor:
Katya Rubinow, MD
Literature review current through: Dec 2022. | This topic last updated: Jun 29, 2021.

INTRODUCTION — All people with diabetes mellitus who use insulin and some people who take other glucose-lowering medications that can cause hypoglycemia should monitor their glucose concentrations to help maintain safe, target-driven glucose management. The effectiveness of self-monitoring in patients with type 2 diabetes who use glucose-lowering agents not likely to result in hypoglycemia is less certain. For these individuals, a targeted, personalized approach is preferred.

Several practical points about glucose monitoring will be reviewed here, including the optimal frequency of monitoring, accuracy of glucose meters and glucose test strips, the accuracy of the operator, the efficacy, reliability, and role of continuous glucose monitoring (CGM) systems, and how to use the glucose information that is obtained. The use of glycated hemoglobin (A1C) measurements to estimate mean blood glucose and studies evaluating the efficacy of automated, closed-loop system of insulin delivery based upon continuous glucose sensing are reviewed separately. (See "Measurements of glycemia in diabetes mellitus" and "Continuous subcutaneous insulin infusion (insulin pump)".)

Glucose monitoring during pregnancy and in the inpatient setting also are reviewed separately. (See "Gestational diabetes mellitus: Glucose management and maternal prognosis", section on 'Glucose monitoring' and "Pregestational (preexisting) diabetes mellitus: Antenatal glycemic control", section on 'Blood glucose monitoring' and "Management of diabetes mellitus in hospitalized patients".)

TYPE 1 DIABETES

Frequency of monitoring — For people with type 1 diabetes, monitoring of glucose is widely accepted as beneficial [1]. Frequent testing of glucose levels is necessary to achieve A1C targets safely without frequent or severe hypoglycemia. Self-monitoring allows adjustments of doses and timing of insulin as well as the timing and content of meals and snacks based on immediate feedback of glucose results. It allows timely intervention for low or decreasing glucose levels to avert serious hypoglycemic events. Monitoring will be effective only if the patient and provider use the information to make appropriate dietary or therapeutic adjustments.

People with type 1 diabetes may use blood glucose monitoring (BGM) with fingersticks and a glucose meter, and/or continuous glucose monitoring (CGM). CGM is generally used in people with type 1 diabetes, if available and affordable.

Because of reliability issues (particularly in the hypoglycemic ranges), warm-up times, and the need to calibrate some CGM devices, CGM does not eliminate the need for at least occasional fingersticks (BGM).

BGM For people using BGM without CGM, testing at home should be done at least four times daily (before meals and at bedtime), occasionally postprandially (90 to 180 minutes after meals), prior to exercise, and, occasionally for safety, at 3 AM. The frequency of testing may vary based on individual needs. Patients with hypoglycemia unawareness may need to test more frequently, particularly prior to driving or operating any machinery, watching small children, and other activities where compromise of cognitive function may be dangerous. The American Diabetes Association (ADA) endorses BGM in type 1 diabetes as noted and, in addition, when low blood glucose is suspected and after treating low blood glucose (until glucose levels are normal) [2]. This can require checking as often as 6 to 10 times daily in some patients on specific days, but the frequency can vary between individuals and in the same individual on different days. (See 'BGM systems' below.)

CGM – For people with type 1 diabetes using CGM, consistent use of CGM provides the greatest glycemic benefits [2,3]. In addition, patients (and/or their caregivers) must understand the technology and should be able to analyze data and use the trending information provided by CGM to make insulin adjustments (eg, a mealtime insulin dose could be reduced if the trend on the CGM device shows a brisk downward trend) [4,5]. All CGM devices require some BGM tests during CGM warm-up periods, when CGM cannot be used, and to double-check selected high and low CGM values, and some CGM devices still require BGM testing for calibration. (See 'CGM systems' below.)

Benefits of CGM — Continuous glucose monitoring (CGM) has the greatest potential benefit for improving safety in patients with nocturnal hypoglycemia, hypoglycemic unawareness, and/or frequent episodes of hypoglycemia [6-8]. CGM is a tool, not a therapeutic intervention. It provides important information with which motivated patients can modify their behavior, improve their A1C values, and increase the percent of glucose readings in the target range safely while reducing hypoglycemia risk. CGM remote data sharing also has the potential to provide health benefits and improve quality of life in selected individuals [9]. Although CGM is not yet generally recommended for the inpatient or critical care setting, it has been used in inpatient locations more frequently since the onset of the coronavirus 2019 (COVID-19) pandemic. (See "COVID-19: Issues related to diabetes mellitus in adults" and "Management of diabetes mellitus in hospitalized patients", section on 'Blood glucose monitoring'.)

In a 2017 meta-analysis, CGM compared with BGM modestly improved glycemic management (mean reduction in A1C approximately 0.3 percentage points) [10]. In subsequent trials in adults primarily treated with multiple daily injections, compared with BGM, CGM improved A1C and/or reduced some measures of hypoglycemia [6,11-18]. As examples:

In one of the trials, 158 adults with type 1 diabetes (mean A1C 8.6 percent), were randomly assigned to CGM or usual care (BGM at least four times daily) [11]. The usual care group wore CGM for data collection for 14 days during the 24-week study but were masked to the results. Patients in the CGM group verified the CGM glucose value with the blood glucose meter prior to injecting insulin. Patients in the CGM group performed a mean of 3.6 fingersticks daily, compared with 4.6 per day in the control group.

After 24 weeks, the reduction in A1C was greater with CGM (1.0 versus 0.4 percentage points, respectively). Median duration of hypoglycemia (<70 mg/dL) was lower in the CGM group (43 versus 80 minutes per day). The incidence of severe hypoglycemia was low and did not differ between the two groups.

Another trial was an open-label crossover trial in which 161 adults with type 1 diabetes (mean A1C 8.6 percent) were randomly assigned to CGM or conventional monitoring with a washout period of 17 weeks [13]. Mean A1C was lower during CGM (7.92 versus 8.35 percent). The mean percentage of time spent in a hypoglycemic range (<70 mg/dL) was lower in the CGM group (2.79 versus 4.79 percent). There were one and five severe hypoglycemic events during CGM and conventional monitoring, respectively, during the 26-week study. Patients in the CGM group performed a mean of 2.75 fingersticks daily, compared with 3.66 per day in the control group.

In a third trial, patients with type 1 diabetes and a history of impaired hypoglycemic awareness or severe hypoglycemia during the previous year wore a masked CGM system for 28 days and then were randomly assigned to unmasked CGM versus BGM [6]. The primary outcome, hypoglycemic events per 28 days, was defined as glucose values of ≤54 mg/dL (3 mmol/L) for at least 20 minutes, preceded by a minimum of 30 minutes with glucose values >54 mg/dL. There was a greater reduction in the primary outcome in the CGM group (10.8 to 3.5 versus 14.4 to 13.7 events, respectively). There was also a significant reduction in the number of nocturnal hypoglycemic events in the CGM but not the control group. A1C values remained similar in both groups.

In all three trials, satisfaction with CGM use was high.

TYPE 2 DIABETES

Who should self-monitor? — Blood glucose monitoring (BGM) is useful in people with type 2 diabetes who take medications that can cause hypoglycemia and/or need to be adjusted based on ambient glucose levels (see 'Frequency of monitoring' below). BGM is generally unnecessary in patients who are treated with diet alone or who take oral or injectable agents that do not cause hypoglycemia, especially if they have achieved their treatment goals (see 'Non-insulin treated' below). However, even in these patients, periodic BGM is often recommended during intercurrent illnesses or if symptoms of hyperglycemia develop.

Frequency of monitoring — The frequency of BGM in people with type 2 diabetes, while most often less than for people with type 1 diabetes, is dependent on the glycemic targets set and the treatments used. The frequency of testing may vary based on individual needs.

Insulin treated

Intensive insulin regimens – For people with type 2 diabetes who take basal and prandial insulin, with adjustment of the dose based on ambient glucose levels and the timing and content of meals, the optimum frequency of BGM is similar to that used in type 1 diabetes (at least four times daily, before meals and at bedtime).

Basal insulin – People with type 2 diabetes who take basal insulin and need to adjust the dose based on ambient glucose levels should test blood glucose at least once daily (fasting) and sometimes before dinner or bedtime (and at other times if hypoglycemia is suspected). Glucose levels are characteristically more stable in basal insulin-treated type 2 diabetes, and such patients usually require less frequent monitoring than in type 1 diabetes. However, if the A1C is elevated in the presence of a fasting glucose within target range, postprandial hyperglycemia is likely. Additional checking (eg, two to three hours after eating) can be useful to direct change in therapy. (See "Insulin therapy in type 2 diabetes mellitus", section on 'Persistent elevation in A1C with fasting glucose in target range' and "Cases illustrating blood glucose monitoring in type 2 diabetes".)

Use of CGM – CGM is used infrequently in people with type 2 diabetes not treated with intensive insulin therapy. It is an option for people with type 2 diabetes treated with multiple daily insulin injections (basal/bolus insulin therapy) who need to adjust the dose of insulin based on glucose levels, particularly in those with frequent hypoglycemia or hypoglycemic unawareness [2,8,19,20]. For individuals who have not reached their treatment goals or are making changes in their treatment regimen, intermittent, targeted use can help identify glycemic patterns that direct changes in behaviors and/or pharmacologic therapy. Periodic use of CGM can identify glycemic patterns that direct timing of BGM. For example, the demonstration of hyperglycemia after breakfast may lead the individual to change the carbohydrate composition of breakfast, and then to assess the effectiveness of this intervention by performing BGM before and two to three hours after breakfast.

There are fewer trials evaluating CGM in patients with type 2 diabetes [21-27]. In one meta-analysis, there was a significant reduction in A1C with use of CGM versus BGM in adults with type 2 diabetes (weighted mean difference -0.7 percent [95% CI -1.14 to -0.27]) [25]. Severe and nocturnal hypoglycemia were infrequent in both groups.

In subsequent trials in patients treated with multiple daily injections of insulin (n = 158) or with basal insulin (n = 175), CGM compared with BGM reduced A1C (adjusted mean difference -0.3 percentage points [95% CI -0.5 to 0.0 percent] at 24 weeks and -0.4 percentage points [95% CI -0.8 to -0.1 percent] at 8 months, respectively) [21,24]. The CGM group also had a higher percentage of time in the target glucose range (59 versus 43 percent, mean difference 15 percent [95% CI 8-23 percent]). There was no difference in total insulin doses or medication adjustments, suggesting that glycemic improvement was related to improved adherence to medication, dietary, and/or exercise regimens [24]. Severe hypoglycemia (percent time <54 mg/dL) was infrequent in both groups [21,24]. In one trial, quality-of-life measures did not significantly differ between the groups [21]. Physicians who provided care for the patients and were recompensed by the sponsor (the device maker) were not masked to the treatment assignment. This potential source of bias, the relatively short duration of both studies, and the absence of any obvious explanation for the modest reduction in A1C should all temper enthusiasm for using CGM in type 2 diabetes for now.

Non-insulin treated — BGM is less effective in improving glycemic management in people with type 2 diabetes not receiving insulin [28]. It may be useful for safety in patients who take medications that can cause hypoglycemia. In our experience, it may also be useful as part of a patient education strategy emphasizing the effects of diet, physical activity, and diabetes medications on blood glucose.

Drugs that can cause hypoglycemia – Patients treated with sulfonylureas or meglitinides, which can cause hypoglycemia, should be tested once to twice per day during titration of their doses but, after a stable dose and target glycemic targets are achieved, may only need to test several times per week, usually in the morning or before dinner, or at times when hypoglycemia is suspected. Patients taking sulfonylureas or meglitinides should consider testing more frequently before driving and during long periods of driving, on sick days, and when there are changes in diet and exercise patterns. This is especially appropriate if they have a history of hypoglycemia or A1C levels close to target (eg, ≤7 percent).

Drugs that do not cause hypoglycemia, or diet treated – BGM may not be necessary (or only in unusual circumstances) for people with type 2 diabetes who are diet treated or who are treated with diabetes agents not associated with hypoglycemia and have achieved their glycemic goals. As an example, BGM may be unnecessarily burdensome in frail, older individuals with cognitive impairment or difficulty with fine motor skills from neurologic or musculoskeletal conditions. In such patients, the target for A1C should be somewhat higher (≤8 percent) than for younger and more fit older patients, and therefore, there usually is less of a role for regular BGM. However, in our experience, BGM may be useful for some people with type 2 diabetes who would take action to modify eating patterns or exercise, as well as be willing to intensify pharmacotherapy based on BGM results.

In meta-analyses of trials comparing BGM with no BGM in non-insulin-treated people with type 2 diabetes, there was improvement in A1C (approximately -0.3 percentage points) in the short term (12 to 24 weeks) [29-31], but there was no difference at one year [29,31]. In a subsequent one-year trial comparing glycemic management, adverse effects (hypoglycemia), and health-related quality of life with BGM versus no BGM, there were no differences in any of the outcomes with BGM (even when combined with enhanced patient feedback) [28]. There are no data showing that BGM affects long-term, clinically important outcomes (eg, diabetes complications).

BGM is expensive. In an economic analysis of BGM in non-insulin-treated type 2 diabetes using data from a United Kingdom trial [32], BGM was associated with diminished initial quality of life and was considered unlikely to be cost effective [33].

BGM SYSTEMS — Blood glucose monitoring (BGM) requires fingersticks for capillary blood sampling and the use of a glucose meter.

Blood glucose meters — There are a variety of BGM systems available. They should be approved by either the International Organization for Standardization or the US Food and Drug Administration (FDA) [2]. Many current glucose meters are reasonably accurate (±10 percent) and require a very small drop of blood. In an evaluation of the accuracy of 18 approved monitoring systems, only six met accuracy standards in all three studies, five met them in two studies, and three in one study (four did not meet accuracy standards in any of the three studies) [34]. While these represent findings from a single study, it is important to be aware that blood glucose meter accuracy, in particular during episodes of hypoglycemia and in patients with poor peripheral tissue perfusion, may be less than optimal [35-37].

Although glucose meters measure capillary blood glucose, almost all available glucose meters provide plasma equivalent values rather than whole-blood glucose values. Thus, results from most available glucose meters and commercial laboratories should be comparable.

Glucose strips — Some glucose strips have considerable batch-to-batch variation and require recalibration to a meter every time a new batch is used. Many strips are packaged in groups (10, 25, 50, or 100) inside a canister containing a desiccant to control humidity. Common errors include leaving the lid off for periods of time (with exposure to heat, moisture, and humidity), use of expired strips, and mixing lots of different strips in one can for convenience. Patients may forget to match the code on the strip bottle to the meter code, with uncompensated batch variation causing erroneous glucose value readings. Fortunately, most meters now have eliminated the need to code each bottle of strips. Most newer meters overcome this problem by automatically recognizing codes for strips.

Site of testing — Several blood glucose meters are now available that use sites other than the finger to obtain blood samples in an effort to reduce the discomfort involved with fingersticks. A study of one device that can be used to obtain samples from the arm found that it provided accurate results and was less painful than fingerstick testing [38].

Monitoring from alternate sites, such as the skin of the forearm, may give slightly lower results than those taken at the fingertips since they may sample venous blood rather than capillary blood. While this should not be a problem if the patient uses one or the other site exclusively, the between-test variability will increase if numerous sites (such as fingertips and forearm sites) are used. In addition, during times when the blood glucose concentration is either rising rapidly (such as immediately after food ingestion) or falling rapidly (in response to rapidly acting insulin or exercise), blood glucose results from alternate sites may give significantly delayed results compared with fingerstick readings (figure 1) [39,40].

Potential errors — Errors in BGM are most frequently attributed to operator error [41]. Problems arise from failure to use test strips appropriate to the meters or calibrate the meter correctly, dirty meters, improper storage of the test strips, poor skin preparation (cleansing), or use of expired strips. Some substances (eg, uric acid, acetaminophen, maltose, and ascorbic acid) can interfere with glucose readings, depending on the chemical reaction of that particular strip [2].

Patients who are motivated and test often usually get much more reliable results than those who are less interested or who test less frequently [42].

We also recommend the following steps to increase the accuracy of glucose monitoring:

The glucose meter and strips should be brought in for clinic visits. The patient's method of testing should be observed periodically and any technical mistakes corrected. Patients should be queried regarding storage of strips.

If BGM results do not seem consistent with expectations, we recommend that the patient bring the glucose meter in to be checked against meters of known accuracy or with a simultaneous laboratory value.

Glucose data from most meters can be downloaded using widely available software, so that the actual measurements can be reviewed (rather than relying on patients' self-report of frequency of testing and specific results). Review of downloaded measurements allows for more accurate review of data than may be available from patient recall. When using downloaded data, it is important to appreciate that the time and date in the meter may need to be reset and corrected. (See 'Using the information' below.)

CGM SYSTEMS

Devices — Continuous glucose monitoring (CGM) devices measure the glucose content of interstitial fluid (which correlates well with plasma glucose, albeit with a 10- to 15-minute delay when blood glucose values are changing rapidly). Glucose levels are measured every 5 to 15 minutes, depending on the device.

For most CGM devices, interstitial fluid is accessed by an electrochemical enzymatic sensor inserted subcutaneously by the patient and changed every 7 to 14 days. Glucose readings are automatically transmitted to a device-specific receiver, smartphone, smart watch, or other smart device. Alternatively, a fluorescence-based sensor can be implanted subcutaneously by a health care professional [43]. A transmitter (placed on the skin) is attached to the sensor (or worn over the sensor), and it transmits the glucose data to a receiver/smartphone. The implanted sensor needs to be replaced after 90 days. The transmitters are replaced at intervals that are device specific.

CGM systems provide visualization of the current glucose value as well as trend arrow analysis, which indicates the direction of changing glucose. This technology can help patients fine-tune dosing [4,5]. There are two main types of CGM systems: "real time" and devices that require intermittent scanning. Each of these types is available for personal and professional use. Professional CGM are devices the patient receives from their health provider's office for short-term use. Devices can be worn "blinded" (no information available to the patient while wearing the device) or unblinded. Patients are instructed to log their meals, exercise, and insulin doses. Devices are returned, downloaded in the clinician's office, and data are reviewed with the patient, providing useful information about the frequency of unrecognized hypoglycemia and hyperglycemia and the extent of within-day and between-day variations in blood glucose.

Real time – Real-time CGM devices measure and transmit glucose values every five minutes. All of the real-time CGM devices alert (alarm) for hypoglycemia or hyperglycemia. The immediate feedback of glucose results allows timely intervention for rising or low/decreasing glucose levels to aid management and avert serious hypoglycemic events. Glucose values can be automatically and securely shared with a clinician via mobile medical glucose-monitoring applications downloaded on to a mobile device, such as a smartphone and web-based diabetes-management software [44]. Many CGM devices also allow individuals to share their glucose data in real time with friends, relatives, or caregivers using a smartphone app. This feature may be particularly important to alert caregivers and friends when an individual has hypoglycemia.

Requirements for confirmatory fingerstick glucose measurements (for calibration and/or prior to making treatment decisions) vary with the CGM device. Some devices are factory calibrated, but other real-time CGM devices still require some blood glucose monitoring (BGM) testing for calibration. Several devices do not require fingerstick glucose determinations for confirmatory measurements prior to making insulin dosing decisions [45], whereas others do.

BGM may also be needed during sensor warm-up periods, when glucose levels are rapidly changing, as well as when the patient suspects hypoglycemia or sensor inaccuracies. In one study, using an older CGM device with an enhanced algorithm, CGM without confirmatory BGM was as safe and effective as using it with BGM [46,47].

Intermittently scanned – Intermittently scanning CGM devices (also called flash CGM) measure glucose every minute and record measurements every 15 minutes. They can be worn for up to 14 days. To view recent glucose readings and trend arrows, the user swipes a reader over the sensor/transmitter, which is worn on the arm. Only the last eight hours of glucose readings are reported on the device or smartphone graph (ambulatory glucose profile). If the sensor is not scanned at least every eight hours, data are lost. The early model has no alarms for hyper- or hypoglycemia, and the person can use their smartphone as the "reader." In a later model, optional real-time glucose alarms are available. Fingerstick glucose determinations are not needed for calibration or confirmation of routine blood glucose values [48,49]. In the United States, the flash CGM is less expensive than real-time CGM devices.

CGM integrated with insulin pump therapy ("artificial pancreas") is reviewed separately. (See "Continuous subcutaneous insulin infusion (insulin pump)".)

Download display — CGM devices can be downloaded and patterns of hypoglycemia and hyperglycemia examined (figure 2). For example, hyperglycemia after lunch would suggest the need to either administer more insulin with lunch or reduce the carbohydrate content of lunch.

Standardization of glucose reporting has been recommended in the form of an Ambulatory Glucose Profile (figure 3). This display contains graphics as well as glucose metrics: mean glucose, time (percent) in target range (70 to 180 mg/dL [3.9 to 10 mmol/L]), time (percent) in hypoglycemia (<70 mg/dL [3.9 mmol/L], <54 mg/dL [3.0 mmol/L]), and time (percent) in hyperglycemia (>180 mg/dL [10.0 mmol/L]) and >250 mg/dL (13.9 mmol/L)] [50]. Target ranges can be changed for specific patient populations (eg, lowered during pregnancy or raised for the frail older adult). Glucose variability is reported by standard deviation and percent coefficient of variation. The glucose management indicator (GMI) can be calculated from at least 10 days of CGM data (preferably ≥14 days). GMI is a new measure that estimates A1C from mean CGM glucose [51]. The GMI-estimated A1C uses a conversion formula based on updated clinical trials and modern-day CGM devices. It may be similar, higher, or lower than laboratory A1C values.

For adults using insulin pump therapy, data displays of CGM, BGM, basal insulin infusion, and insulin bolus delivery together over time may be particularly helpful to identify glycemic patterns and direct changes in therapy (figure 4).

Reliability — The interstitial fluid glucose sensor yields lower glucose values compared with venous plasma glucose when blood glucose concentrations are rapidly rising, owing to delayed equilibration between the different physiologic compartments (figure 5) [52]. CGM is less accurate in the extreme low (<40 mg/dL [2.2 mmol/L]) and high (>400 mg/dL [22 mmol/L]) glucose ranges, but overall accuracy is improving. For the newer devices, the mean absolute relative difference (MARD) is generally <11 percent [53-58]. However, given differences in patient populations, sample sizes, study designs, and methodologies and lack of studies directly comparing different CGMs, comparisons of reliability between the devices are problematic.

Patients taking medications containing acetaminophen or treated with high-dose vitamin C may experience falsely elevated CGM glucose values with some, but not all, CGM devices. This is a dose-dependent effect (depending on acetaminophen tissue levels), which results from oxidation of acetaminophen by CGM electrodes [59].

USING THE INFORMATION — For most patients with type 1 diabetes, continuous glucose monitoring (CGM) or blood glucose monitoring (BGM) results before and at intervals after meals, before, during, and after exercise, and occasionally during the night provide useful information for adjusting insulin regimens and other behaviors that influence glycemic management. Additionally, monitoring (particularly real-time CGM) can be very useful to avoid and/or help treat potentially dangerous hypoglycemia. CGM is also useful for detecting previously unrecognized hypoglycemia. In addition, the real-time use of CGM trend arrows can assist patients to more accurately bolus (or inject) insulin for meals and correction, thereby preventing hypoglycemia and reducing hyperglycemia. (See "Cases illustrating problems with insulin therapy for type 1 diabetes mellitus", section on 'Case 3: Morning hyperglycemia'.)

This regimen will be effective only if the patient is able to use the information to make appropriate dietary or therapeutic adjustments. Many glucose meters/CGM systems provide data management features that can be downloaded onto a computer, with graphic representation of glycemic variation by time of day or over a period of weeks, allowing for calculation of means and visualization of trends and variances. Pattern recognition may be improved if results are recorded in a diary that includes information on food intake, physical activity, and insulin dosing, which can be examined on a regular basis.

Optimal use of the data obtained is best done in two stages, both in conjunction with patient education:

Pattern identification – Patterns, as opposed to intermittent problems, are best visualized with CGM because there are a relatively large number of measurements. If using BGM, blood glucose values should be recorded four to seven times daily for several days and evaluated for patterns of variation, which allow adjustment of doses or types of insulin at different times of the day.

Insulin algorithms – Once a basic regimen of eating, exercise, and insulin dosing has been established, there will still be day-to-day variability in blood glucose values due (among other factors) to exercise, stress, and the vagaries of insulin and food absorption. (See "Management of blood glucose in adults with type 1 diabetes mellitus".)

Insulin dosing decisions can be effectively made using an insulin algorithm in which the before-meal dose of rapid-acting insulin is adjusted according to the blood glucose value using a correction factor (or insulin sensitivity factor), target glucose, and anticipated carbohydrate content of the meal. Changes in exercise and use of CGM trend arrows can also be included in this calculation. The adjustments should be small in patients who are very sensitive to insulin or who are taking low doses of insulin (eg, with subcutaneous, continuous insulin infusion via a pump). (See "Nutritional considerations in type 1 diabetes mellitus", section on 'Insulin dosing' and "Cases illustrating problems with insulin therapy for type 1 diabetes mellitus", section on 'Case 6: Late afternoon hypoglycemia'.)

Patient education – If BGM/CGM is initiated to improve glycemic management, patient education strategies are necessary to ensure successful management of BGM/CGM feedback [60]. In one small, longitudinal study of patient views on BGM, the frequency of testing decreased over time, often because patients did not know how to respond to high readings, and patients perceived that providers were more interested in A1C values than glucose logs [61]. In another study, use of BGM was successful in reducing A1C values when accompanied by training of patients and clinicians to collect and interpret BGM profiles [62]. Similarly, CGM is only beneficial if patients and/or their caregivers understand the technology and use the information to adjust insulin doses, diet, and/or physical activity. (See 'CGM systems' above.)

With a well-educated and motivated patient, therapeutic advice can often be given remotely by video visit or over the telephone, or even via fax or e-mail. In general, adjustments aimed at preventing/eliminating hypoglycemia are addressed first. It is important not to recommend many changes at the same time. Having made a change, it is usually best to wait several days until the effect of that change can be assessed from further blood glucose measurements.

PATIENTS WITH SPECIAL NEEDS — Visually impaired patients may have difficulty using glucose meters; with help, this problem can be overcome with "talking meters" or large-screen meters. Patients or providers may contact:

American Association of Diabetes Educators (AADE)

200 W Madison Street, Suite 800

Chicago, IL 60606

Tel: 1-800-338-3633

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Blood glucose monitoring".)

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 5th to 6th 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 10th to 12th 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 1 diabetes (The Basics)" and "Patient education: Type 2 diabetes (The Basics)" and "Patient education: Carb counting for adults with diabetes (The Basics)" and "Patient education: My child has diabetes: How will we manage? (The Basics)" and "Patient education: Controlling blood sugar in children with diabetes (The Basics)" and "Patient education: Managing diabetes in school (The Basics)" and "Patient education: Giving your child insulin (The Basics)" and "Patient education: Checking your child's blood sugar level (The Basics)")

Beyond the Basics topics (see "Patient education: Type 1 diabetes: Overview (Beyond the Basics)" and "Patient education: Type 2 diabetes: Overview (Beyond the Basics)" and "Patient education: Blood glucose monitoring in diabetes (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

In patients with type 1 diabetes, frequent testing of glucose levels is necessary to achieve glycated hemoglobin (A1C) targets safely without frequent or severe hypoglycemia. Patients may use blood glucose monitoring (BGM) with fingersticks and a glucose meter, or continuous glucose monitoring (CGM) if available. Because of reliability issues (particularly in the hypoglycemic ranges), warm-up times, and the need to calibrate some CGM devices, CGM does not eliminate the need for at least occasional fingersticks. (See 'Type 1 diabetes' above.)

For patients with type 1 diabetes using BGM without CGM, testing at home should be done at least four times daily (before meals and at bedtime), occasionally postprandially (90 to 180 minutes after meals), prior to exercise, and, occasionally for safety, at 3 AM. The frequency of testing will vary based on individual needs. Patients with hypoglycemia unawareness will need to test more frequently, particularly prior to driving or operating any machinery, watching small children, and other activities where compromise of cognitive function may be dangerous. (See 'Frequency of monitoring' above.)

In patients with type 1 diabetes, CGM compared with BGM has been shown to reduce A1C and episodes of hypoglycemia and improve time in target range modestly. CGM can be particularly useful for improving safety in patients with nocturnal hypoglycemia, hypoglycemia unawareness, and/or frequent episodes of hypoglycemia. All CGM devices require some BGM tests to double-check high and low CGM values, and some CGM devices still require BGM testing for calibration. (See 'Benefits of CGM' above.)

BGM is useful in people with type 2 diabetes who take medications that can cause hypoglycemia and/or need to be adjusted based on ambient glucose levels. BGM is generally unnecessary in patients who are treated with diet alone or who take oral or injectable agents that do not cause hypoglycemia, especially if they have achieved their treatment goals. However, even in these patients, periodic BGM is often recommended during intercurrent illnesses or if symptoms of hyperglycemia develop. CGM is used infrequently in people with type 2 diabetes not treated with intensive insulin therapy. Periodic CGM use may be helpful in identifying glycemic patterns and as part of a patient education program. (See 'Who should self-monitor?' above.)

People with type 2 diabetes who take basal and prandial insulin, with adjustment of the dose based on ambient glucose levels and the timing and content of meals and snacks, should test blood glucose at least four times daily (before meals and at bedtime) and more often before driving, during long periods of driving, on sick days, and when there are changes in diet and exercise patterns. CGM is appropriate for people with type 2 diabetes treated with multiple daily insulin injections, particularly in those with frequent hypoglycemia or hypoglycemic unawareness. (See 'Insulin treated' above.)

People with type 2 diabetes treated with sulfonylureas or meglitinides should test once to twice per day during titration of their doses. After a stable dose and target glycemic targets are achieved, they may only need to test several times per week, usually in the morning or before dinner, or if hypoglycemia is suspected. Patients may need to test more frequently before driving and during long periods of driving, on sick days, and when there are changes in diet and exercise patterns. (See 'Non-insulin treated' above.)

Fully automated, closed-loop systems of insulin delivery based upon continuous glucose sensing are reviewed separately. (See "Continuous subcutaneous insulin infusion (insulin pump)".)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges David McCulloch, MD, who contributed to an earlier version of this topic review.

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Topic 1781 Version 43.0

References