Chapter 9: Monitoring Glycemic Control
Canadian Diabetes Association 2013 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada
Glycated Hemoglobin Testing
- Glycated hemoglobin (A1C) is a reliable estimate of mean plasma glucose (PG) levels over the previous 3 to 4 months for most individuals.
- A1C is the preferred standard for assessing glycated hemoglobin, and laboratories are encouraged to use assay methods for this test that are standardized to the Diabetes Control and Complications Trial (DCCT) reference.
- For most individuals with diabetes, A1C should be measured every 3 months to ensure that glycemic goals are being met or maintained. Testing at least every 6 months should be performed in adults during periods of treatment and lifestyle stability when glycemic targets have been consistently achieved [Grade D, Consensus].
- In Canada, the A1C continues to be reported using the National Glycohemoglobin Standardization Program (NGSP) units (%). To convert NGSP units to International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) SI units (mmol/mol), the following equation can be used: IFCC = 10.93(NGSP) – 23.50 (see Appendix 11 for a conversion chart of A1C from NGSP units to IFCC SI units).
Self-Monitoring of Blood Glucose
- Self-monitoring of blood glucose (SMBG) can serve as a useful adjunct to other measures of glycemia, including A1C. In situations where A1C does not accurately reflect glycemia, SMBG is essential.
- SMBG is the only way to confirm hypoglycemia. It can provide feedback on the results of lifestyle and pharmacological treatments, and increase patient empowerment and adherence to treatment. It can also provide information to patients and health care professionals to facilitate long- or short-term treatment decisions.
- SMBG is most effective when combined with an educational program that incorporates behavioural changes (lifestyle modification and/or oral hypoglycemic agents) in response to BG values.
- Patients should receive instruction on (1) how and when to perform SMBG, (2) how to record the results in an organized fashion, (3) the meaning of various BG levels, and (4) how behaviour and actions affect SMBG results.
Frequency of SMBG
- The recommended frequency of SMBG must be individualized to each person's unique circumstances.
- Factors influencing this recommendation will include type of diabetes, type of therapy, adequacy of glycemic control, literacy and numeracy skills, propensity to hypoglycemia, awareness of hypoglycemia, occupational requirements and acute illness.
- In many situations, for all individuals with diabetes, more frequent testing should be undertaken to provide information needed to make behavioural or treatment adjustments required to achieve desired glycemic targets and avoid risk of hypoglycemia [Grade D, Consensus].
Type 1 and type 2 treated with insulin
- For individuals using insulin more than once a day, SMBG should be used as an essential part of diabetes self-management [Grade A, Level 1, for type 1 diabetes; Grade C, Level 3, for type 2 diabetes] and should be undertaken at least 3 times per day [Grade C, Level 3] and include both pre- and postprandial measurements [Grade C, Level 3].
- In those with type 2 diabetes on once-daily insulin in addition to oral antihyperglycemic agents, testing at least once a day at variable times is recommended [Grade D, Consensus].
- In a large cohort study, performance of ≥3 self-tests per day was associated with a statistically and clinically significant 1.0% absolute reduction in A1C.
Type 2 diabetes not treated with insulin
- For individuals with type 2 diabetes not receiving insulin therapy, SMBG recommendations should be individualized depending on type of antihyperglycemic agents, level of glycemic control and risk of hypoglycemia [Grade D, Consensus].
- When glycemic control is not being achieved, SMBG should be instituted [Grade B, Level 2] and should include periodic pre- and postprandial measurements and training of health care providers and patients on methods to modify lifestyle and medications in response to SMBG values [Grade B, Level 2].
- If achieving glycemic targets or receiving medications not associated with hypoglycemia, infrequent SMBG is appropriate [Grade D, Consensus].
- A series of recent meta-analyses have generally shown a small benefit to reducing A1C, with (absolute) A1C reductions of 0.2% to 0.5%, in individuals with type 2 diabetes treated with lifestyle management, with or without oral antihyperglycemic agents performing SMBG compared to those who did not. A1C reduction was greater in those performing SMBG when the baseline A1C was >8%.
- SMBG has been demonstrated to be most effective in persons with type 2 diabetes within the first 6 months after diagnosis.
- There is no evidence that SMBG affects patient satisfaction, general well-being or general health-related quality of life.
Verification of accuracy of SMBG performance and results
- In order to ensure accuracy of BG meter readings, meter results should be compared with laboratory measurement of simultaneous venous FPG at least annually and when indicators of glycemic control do not match meter readings [Grade D, Consensus].
- Periodic re-education on correct SMBG technique may improve the accuracy of SMBG results.
- In rare situations, therapeutic interventions may interfere with the accuracy of some SMBG devices (e.g. icodextrin-containing peritoneal dialysis). Care should be taken to select an appropriate meter in such situations.
Alternate site testing
- Some meters allow SMBG using blood samples from sites other than the fingertip (forearm, palm of the hand, thigh). Accuracy of BG levels with these meters is variable.
- During periods of rapid change in BG levels (e.g. after meals, after exercise and during hypoglycemia), fingertip testing has been shown to more accurately reflect glycemic status than forearm or thigh testing.
- Blood samples taken from the palm near the base of the thumb (the thenar area) demonstrate a closer correlation to fingertip samples at all times of day and during periods of rapid change in BG levels.
- Individuals with type 1 diabetes should be instructed to perform ketone testing during periods of acute illness accompanied by elevated BG, when preprandial BG levels remain >14.0 mmol/L or in the presence of symptoms of diabetic ketoacidosis (DKA) [Grade D, Consensus].
- Blood ketone testing methods may be preferred over urine ketone testing, as they have been associated with earlier detection of ketosis and response to treatment [Grade B, Level 2].
- Symptoms of DKA include nausea, vomiting or abdominal pain. If all of these symptoms present in type 2 diabetes, ketone testing should be considered.
- Testing methods that measure blood beta-hydroxybutyric acid (beta-OHB) levels may provide more clinically useful information than those that measure urine acetoacetate or acetone levels.
Continuous Glucose Monitoring Systems
- Continuous glucose monitoring systems (CGMS) measure glucose concentrations in the interstitial fluid. Two types of devices are available.
- The “real time” (also called “personal”) CGMS provides information directly to the user by displaying moment-to-moment absolute glucose levels and trending artrs, and by providing alarm notifications in the event that the glucose level is above or below a preset limit.
- A “blinded” (sometimes referred to as “professional”) CGMS captures, but does not display, the glucose readings, which are then downloaded onto a computer for viewing and retrospective analysis by the health care provider (typically in conjunction with the user).
- In people with type 1 diabetes, real-time continuous glucose monitoring may be used to improve glycemic control [Grade B, Level 2] and reduce hypoglycemia [Grade B, Level 2].
- CGM provides the best outcomes if it is associated with structured educational and therapeutic programs. CGM is not a replacement for SMBG because SMBG is still required for calibration of the CGM device and, for real-time CGM, to confirm interstitial measurements prior to making therapeutic changes or treating suspected hypoglycemia.
Health Care Provider Tools
For definitions of the levels of evidence cited in this chapter, please refer to the Guideline Recommendations: Levels of Evidence.
If you would like more details on this topic, including references, please visit the Canadian Diabetes Association Clinical Practice Guidelines: Chapter 9.
For recommendations regarding SMBG, see Appendix 4. For A1C conversion factors (NGSP <-> IFCC units), see Appendix 11.