Wellness iNPractice Diabetes

Blood Glucose Monitoring for Assessment of Glycemic Control

Blood glucose levels can be affected by a number of factors, including the amount and type of food intake, physical activity, medications, and comorbid conditions. Glucose monitoring—either by the patient with self-monitoring of blood glucose (SMBG) or by the provider with measurement of A1C—is important to help guide and evaluate diabetes management goals. Achievement of glycemic goals can be partially attributed to the efficacy of the diabetes treatment, diet, and exercise plan.1 The integration of glucose monitoring results into the diabetes management plan may help guide nutritional therapy, physical activity recommendations, and adjustment of pharmacological therapy.  

Self-monitoring of Blood Glucose

SMBG measures capillary glucose levels, and allows patients to track blood glucose fluctuations throughout the day, with the frequency and timing of testing dependent on the patient’s specific needs and goals.1 SMBG is especially important for insulin-treated patients to help monitor blood glucose levels and guide treatment.1 Patients who are taking intensive insulin regimens (patients with type 1 or type 2 diabetes taking multiple-dose insulin therapy) may need to perform SMBG testing 6-10 times daily, including prior to meals and snacks, postprandially, at bedtime, prior to exercise, when they suspect low blood glucose, after treating low blood glucose until they are normoglycemic, and prior to critical tasks such as driving.1 The frequency and timing of SMBG should be re-evaluated at each routine visit.1 For some patients, particularly children, teens, and young adults and patients with hypoglycemia unawareness and/or frequent hypoglycemic episodes, continuous glucose monitoring (CGM) may be useful as an adjunct to SMBG.1 For more information about CGM, visit Treatment Options: Devices.

The accuracy of SMBG measurements is dependent on the glucose testing device being used and the patient’s ability to perform the test. It is important to train patients on how to test their blood glucose, and observe them periodically to ensure that they are using the correct technique. It is also critical that patients know why it is important to measure their blood glucose, understand what constitutes an abnormal blood glucose measurement, and what they need to do to bring glucose levels within the recommended range, including adjusting food intake, physical activity, or insulin dose.1

Evidence for the role of SMBG for patients who are not on an intensive insulin regimen, such as those with type 2 diabetes receiving basal insulin or oral agents, is insufficient.1 However, there is evidence of A1C reduction in patients with type 2 diabetes who adjust their basal insulin dose based on fasting glucose levels.

You can find educational information to share with patients about the importance of SMBG, how to test blood glucose, what the results mean, and what to do about abnormal results by clicking here. Patients can keep track of their blood glucose measurements and share their results with their provider at each visit by using a tracking tool such as Blood Sugar Diary.

Blood Glucose Goals for Nonpregnant Adults with Diabetes1  

Preprandial capillary blood glucose 80-130 mg/dL (4.4-7.2 mmol/L)a
Peak postprandial capillary blood glucoseb <180 mg/dL (<10.0 mmol/L)a
A1C <7.0% (53 mmol/mol)a,c

a More or less stringent glycemic goals may be appropriate for individual patients, based on duration of diabetes, age/life expectancy, comorbid conditions, known cardiovascular disease (CVD) or advanced microvascular complications, hypoglycemia unawareness, and other considerations.

b Postprandial glucose may be targeted if A1C goals are not met despite reaching preprandial glucose goals. Postprandial glucose should be measured at peak glucose levels in patients with diabetes, which are typically seen 1-2 h after the beginning of the meal.

c Lowering A1C to approximately ≤7% has been shown to reduce microvascular complications of diabetes and long-term reduction of macrovascular disease. More stringent A1C goals (such as <6.5%), if this can be achieved without significant hypoglycemia or other adverse events, may be warranted for selected individual patients with short duration of diabetes, type 2 diabetes treated with lifestyle or metformin only, long life expectancy, or no significant CVD. Less stringent A1C goals (such as <8%) may be appropriate for patients with a history of severe hypoglycemia, limited life expectancy, advanced microvascular or macrovascular complications, extensive comorbid conditions, or long-standing, poorly controlled diabetes despite self-management education, glucose monitoring, and multiple glucose-lowering agents including insulin.1

Measuring A1C

A1C is a measurement of glucose that is bound to hemoglobin in red blood cells and reflects average glycemia over several months.2 A1C testing should be performed regularly in all patients with diabetes to evaluate whether patients’ glycemic targets have been reached and maintained.1 Frequency of A1C testing may vary; for patients with stable glycemia, A1C testing twice a year may be sufficient, whereas for patients with unstable glycemia or on intensive regimens, more frequent testing, every three months, may be needed.1 A1C does not provide a measure of day-to-day glycemic fluctuations, and should be considered along with SMBG measurements in patients with type 1 diabetes or with type 2 diabetes who are on intensive insulin regimens.1 A1C results complement those of SMBG to indicate whether diabetes treatment needs to be adjusted to achieve glycemic control.2 A1C testing may also indicate discrepancies in SMBG measurements and whether the frequency and timing of SMBG should change.1 Note that conditions that affect red blood cell turnover and hemoglobin variants (anemia, bleeding, kidney or liver disease) can affect the accuracy of A1C testing.1,2

SMBG Compared with A1C Measurements

Estimated Average Glucose

Based on the results of two large clinical trials, the American Diabetes Association (ADA) and the American Association for Clinical Chemistry found a linear correlation between A1C and blood glucose measurements (by both SMBG and CGM) that allow A1C to be reported as an estimated average glucose (eAG).1 The eAG uses the same units for glucose concentration as SMBG (mg/dL or mmol/L). By using a unit of measurement that is already familiar to patients who do SMBG, patients may find it easier to understand how their A1C value is related to daily blood glucose measurements.

Mean Glucose Levels for Specified A1C Levels1

a These estimates are based on data from >2,700 glucose measurements taken over 3 months per A1C measurement in 507 adults with type 1, type 2, and no diabetes. The correlation between A1C and average glucose was 0.92.3

You can use this calculator to convert A1C results into average glucose levels:

A1C: %
Your average blood sugar level: