University of Toronto - Faculty of Medicine

 

Author
The revision of this chapter was prepared by Jan Glozier, RN, CDE

The Diabetes Control and Complications Trial and the United Kingdom Prospective Diabetes Study demonstrated the relationship between optimal glycemic control and reduced risk for development of microvascular and macrovascular complications in patients with type 1 and type 2 diabetes. Regular evaluation of glycated hemoglobin levels and self-monitored blood glucose results provide the client and health care provider with valuable information regarding the individual's level of glycemic control.

 

• Self-Monitoring of Blood Glucose is an essential component in the management of diabetes and is beneficial for all persons with diabetes.
• Provides feedback to the individual on their level of glycemic control and the effect of alterations to diet, exercise and medication regimen on blood glucose levels.
• Assists health care provider and client in making timely adjustments to the treatment regimen in an effort to achieve blood glucose targets.
• SMBG can alert the client to episodes of hypoglycemia and hyperglycemia.

Barriers to performing SMBG

• Timing, complexity and inconvenience of testing.
• Physical and psychological discomfort associated with blood glucose testing.
• Financial cost of test strips, meter, lancing supplies and batteries.
• Lack of knowledge and/or support on how to interpret blood glucose results and make adjustments to treatment regimen.

Patient Education:

• Patient education and training is fundamental for optimizing the benefits of SMBG
• Motivation to test is dependent on comprehension of the value of testing on their diabetes management.
• Meter results are dependent on the user's knowledge, skill and technique
• Clients must receive proper instruction on the use of SMBG
• The meter selected should be suitable to the client's specific needs and abilities.

Patient education should focus on the following information:

• Individualized blood glucose goals and testing times.
• Guidelines on interpreting blood glucose results and identifying patterns in blood glucose values
• Information on making appropriate adjustments to their diet, activity or treatment regimen based on blood glucose patterns.
• Those taking insulin should be taught to make adjustments to their insulin dose based on changes in food intake, activity or during periods of illness.
• Periodic monitoring of overnight blood glucose levels to assess/prevent nocturnal hypoglycemia
• The need to contact the health care team when problems with glycemic control have been identified.

Frequency of Testing

• The frequency of SMBG should be sufficient to enable the client to achieve optimal level of glucose control.
• The frequency and timing of glucose monitoring should be individualized based on the type of diabetes, treatment regimen, client's individual goals, and level of glycemic control.
• Evidence is less clear regarding frequency of testing in Type 2 diabetes than in Type 1 diabetes.

When choosing the frequency of glucose monitoring, the following should be considered.

Type 1 diabetes:

• SMBG > 3 times/day has been associated with a statistically significant 1.0% reduction in A1C
• In type 1 diabetes postprandial lunch and dinner and bedtime tests have the best correlation to A1C levels.
• Monitoring should include routine fasting, preprandial and periodic 2-hour postprandial blood glucose tests.
• More frequent testing provides helpful information to reduce hypoglycemia risk and adjust therapy

Type 2 diabetes:

• SMBG > 1 time/day has been associated with a statistically significant 0.6 % reduction in A1C in clients treated with oral antihyperglycemic agents.
• Postprandial BG tests demonstrate the best correlation to A1C levels in patients with type 2 diabetes.
• Monitoring should include levels one to three times daily, testing at staggered times including both preprandial and postprandial tests.

Pregnancy and diabetes:

• SMBG is essential during pregnancy in individuals with pre-existing or gestational diabetes.
• The recommended frequency of SMBG is > 4 times per day.
• Clients with type 1 or type 2 diabetes should routinely monitor preprandial and postprandial levels .

Exercise:

• SMBG before, during and after exercise is recommended for clients taking insulin or oral antihyperglycemic agents to determine the impact of exercise on blood glucose levels.

TABLE 10.1 Recommended Frequency and Timing of SMBG and Ketone Testing for Self Management
Type of diabetes or treatment regimen	Frequency	Preprandial and bedtime testing	Postprandial testing	Nocturnal testing at peak of insulin action	Ketone testing
Type 1	At least 3 times per day	Regular testing	Intermittent testing		During illness, symptoms of DKA or BG levels >14.0 mmol/L
Type 2 using insulin	At least 3 times per day	Regular testing	Intermittent testing
Intensive Insulin therapy (MDI or insulin pump)	4 or more tests per day	Regular testing	Intermittent testing	Periodic testing
Type 2 using oral antihyperglycemic agents and basal insulin	At least once daily at variable times	Include	Include
Type 2 using oral antihyperglycemic agents or lifestyle alone	Individualize frequency	Include	Include
Pregnant Type 1 or 2	4 or more tests per day	Regular testing	Regular testing	Needed if taking insulin	Include

More frequent testing is recommended in the following situations:

• • With the initiation of insulin or oral antihyperglycemic agent therapy or during periods of dose adjustment
  • During period of illness or acute hyperglycemia
  • Pharmacological therapies are initiated that can decrease the recognition of hypoglycemia (e.g. beta-blockers) or impact on the individual's level of glycemic control (e.g. corticosteroids, sulfonamides, hydrochlorothiazide, atypical antipsychotics, alcohol)
  • In the presence of severe hypoglycemia and hypoglycemia unawareness.

Verification of the accuracy of SMBG Results

• The accuracy of the client's SMBG technique and meter result should be evaluated initially and at regular intervals.
• Comparisons of blood glucose meter results to simultaneous laboratory venous FPG should be done annually and when there is a large discrepancy between meter results and A1C values.
• For glucose levels > 4.2mmol/L, capillary blood glucose correlation should differ by less than 20% of the lab fasting venous measurement.
• Less variability is recommended for blood glucose levels < 4.2 mmol/L.
• Technique should be reviewed if there is poor correlation between meter and laboratory glucose values.

TABLE 10.2 Selection of Glucose Monitoring Device
Selection Criteria	Comments
Characteristics of Meter	Meters measure blood glucose level using color reflectance or sensor technology. Technological advances have resulted in meters that are more user friendly: compact in size, portable, less user dependent, require sample volume of 0.3 -4.0 microlitres and have testing times ranging from 4 - 30 seconds. Many meters have an extended memory capacity of 20 - 3000 tests, including test date and time and PC downloading capabilities. Warranty for the meters range from 3-5 years to a lifetime warranty
Accuracy and Precision	Meters must meet the accuracy, precision and analytic criteria of a total error of <10% for blood glucose ranging from 1.6-22.2mmol/L Performing a blood glucose test using control solution will verify the accuracy of the meter itself but not the actual patient test. Control testing solutions are available for each meter from the manufacturer.
Cost	Meter prices vary from $0 - $59.99 Test strips prices range from $0.74 - $.95 per strip. Lancet prices range from $5.95 - $12.99 per box of 100 lancets.
Coverage	Private Insurance: Coverage for SMBG supplies dependant upon the individual policy. Monitoring for Health Program (Canadian Diabetes Association): Provides assistance for clients on insulin therapy or with gestational diabetes mellitus that do not have any other form of insurance coverage. Covers 75% of the initial cost of the meter (maximum $75.00) and 75% of the ongoing cost of test strips and lancets (maximum $820.00/year). Provincial Drug Benefit Plans: May provide coverage for certain test strips for seniors and clients on social assistance benefits. This should be taken into account when prescribing a meter

Factors Impacting on the Accuracy of the SMBG Result

• Meter: Meter is old, dirty or exposed o extreme temperatures.
• Test strips: The use of expired test strips, improper storage of strips (i.e. exposure to temperature or humidity) and incorrect meter calibration of the test strip lot #
• Sample size error: Insufficient sample volume and poor blood collection technique are the most common types of user errors. Many meters will provide a test result regardless of sample size and will indicate an error only when the sample volume is grossly insufficient
• Misrepresentation of blood sugar results: Clients may falsify test results. One study demonstrated that there was a 26% discrepancy between self-reported BG results and results in meter memory. The health care team can access the memory feature of the blood glucose meter to verify test results.
• Hematocrit: Anemia can falsely elevate and polycythemia can falsely depress the blood glucose values. Results may vary 4 -30% for every 10% change in hematocrit.

Alternate Site Testing

• Alternate site testing meters (to fingertip) are available
• Alternative sites for blood glucose testing include the forearm, upper arm, abdomen, thigh and may be associated with less pain than finger testing.
• Studies have shown that there is a delayed glycemic response associated with alternative site testing during periods of rapid glucose fluctuation. During periods of rapid change in blood glucose concentrations, fingertip testing provides a more accurate indication of glycemic level than results obtained from alternative site testing.
• Blood samples taken from the base of the thumb area of the palm show a closer result to fingertip testing than forearm or thigh testing
• Fingertip testing may be the preferred test for postprandial BG analysis, hypoglycemia detection and when medication action is peaking.

Continuous Glucose Monitoring System (CGMS)

• A device which can continuously monitor interstitial glucose concentration for several days is now available using a glucose oxidase-based platinum electrode sensor that is inserted into the subcutaneous tissue of the anterior abdominal or upper gluteus.
• The sensor takes readings every 10 seconds and interstitial glucose concentrations are calibrated against 2-4 SMBG tests daily. Sensor results are downloaded and can be used to assist the client and health care provider in identifying glucose patterns or trends following the monitoring period.
• Both "Real Time", in which the individual can view the results as they happen, and retrospective sensor systems are available where the results are only seen upon downloading the device.
• Due to the time lag between BG changes and interstitial glucose levels, "Real time" systems display results from 15 to 20 minutes prior to current time and therefore should not be used for immediate treatment decisions or assess safety to drive etc.
• Further research is required to standardize and validate the use of the CGMS as a clinical tool in diabetes management.

 

• The glycated hemoglobin test (AIC) has been shown to predict the risk of the development of chronic complications.
• The A1C level should be measured every 3 months to assess level of glycemic control. It reflects overall glycemic control over the past 3-4 months.
• Testing at 6 month intervals may be considered if A1C is consistently stable and at target
• The rate of formation of glycated hemoglobin is directly proportional to the ambient glucose concentration over the usual 120 day lifespan of erythrocytes.
• The DCCT and UKPDS revealed that any sustained reduction in A1C was associated with an improvement in risk of microvascular complications.
• A1C test assay should be standardized against the DCCT reference.
• A1C may not be reliable in patient with hemoglobinopathy or anemia.

 

• The Glycated Serum Protein (GSP) test indicates the level of glycemic control over the last 1-2 weeks and can be used to assess glycemic control over a short period of time.
• A1C remains the gold standard for accessing the level of glycemic control and risk of chronic complications of diabetes.
• The fructosamine assay is the most commonly used GSP test. A fructosamine assay can be ordered to assess glycemic control in patients with hemoglobinopathy or anemia or in situations where there is a large discrepancy between SMBG results and A1C levels.

 

• Ketone testing is an important tool used to assess the degree of insulin deficiency during periods of acute illness or stress particularly in those with type 1 diabetes.
• Ketone measurement can be obtained through a serum meter test of beta-hydroxybutyric acid or urine ketone test strips that measure acetoacetate or acetone.
• Serum measurement of ketone level is preferred over urine ketone tests as it provides a more accurate indication of ketoacidosis status and is not prone to the false negative and false positive results associated with urine ketone testing.

Ketone testing should be performed in the following situations:

• Illness: During periods of acute illness or stress for clients with type 1 diabetes or type 2 diabetes when glucose levels are consistently elevated over 14 mmol/L and when symptoms of diabetic ketoacidosis, such as nausea, vomiting or abdominal pain are present.
• Exercising: Clients with type 1 diabetes should test for ketones before exercising if their blood glucose is >14 mmol/L. Clients can exercise if test results are negative for ketones. If the ketone test is positive, clients should take extra insulin and delay exercise until they test negative for ketones.
• Pregnancy: Ketone testing is recommended during illness or when blood glucose levels are > 11.1 mmol/L to assess for diabetic ketoacidosis. The presence of ketones significantly increases the risk of fetal morbidity and mortality. Ketone testing may be used to ensure adequate nutritional intake during pregnancy and to assess for starvation ketosis.
• Result Error: Sulfhydryl drugs such as captopril can cause a false positive result and false negative readings can occur if test strips have been exposed to air for an extended period of time.

References

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