Tight control of blood sugar levels is difficult to achieve. Levels can fall too low even with the best adherence to demanding daily self-monitoring schedules.
The proportion of people in the US with a diagnosis of diabetes who undertake self-monitoring of glucose has risen dramatically – from 36% in 1994 to 64% in 2010.
All patients newly diagnosed with type 1 diabetes will receive training on how to do their blood sampling and how to act on readings. Increasing numbers of people with type 2 diabetes – even those who do not need insulin treatment – are also recommended to self-monitor their blood glucose levels.
What is blood glucose self-monitoring?
Self-monitoring requires a drop of blood and allows patients to improve their understanding of their blood glucose levels.
The aim of self-monitoring is to collect detailed information about blood glucose levels over time at multiple points. It helps maintain constant glucose levels and prevent hypoglycemia, and allows the following to be scheduled accordingly:
- The treatment regime/insulin doses
- Dietary intake
- Physical activity.
Such glycemic control is important in the prevention of the long-term complications of diabetes.
In addition to monitoring diabetes treatment effects and identifying blood sugar highs and lows, self-monitoring is a strategy that guides overall treatment goals. Self-monitoring also gives insight into how diet, exercise and other factors, such as illness and stress, affect blood sugar levels.
Self-monitoring helps patients improve their knowledge of glucose levels and the effects of different behaviors on their blood glucose.
Patients on glucose-lowering drugs can take their self-monitoring records to their health care provider, allowing them to measure prescriptions accordingly and recommend any adjustments to diet and exercise.
Strict glycemic control in type 1 diabetes is difficult to achieve – even with good education on self-monitoring, the most frequent measurement does not give enough information to avoid hypoglycemia.
Who should self-monitor blood glucose?
It was previously only people with insulin-treated diabetes – type 1 in particular – who would be recommended to self-monitor their blood glucose levels.
International guidelines now state that there is enough evidence for the benefit of glycemic control to recommend self-monitoring to anyone with diabetes, including those with type 2 diabetes who do not need insulin treatment, as long as there is sufficient healthcare support. Adequate support entails the following:
- The monitoring is incorporated into an education program to promote appropriate treatment adjustments according to blood glucose values
- There is shared management with health care providers to provide a clear set of instructions for acting on results.
The type of diabetes determines how regularly self-measurement is needed. Type 1 diabetes demands several daily measurements whereas insulin-treated type 2 diabetes needs only around two a day. If no insulin treatment is needed, less than daily measurement may be sufficient.
Target blood glucose levels
The overall goal of glycemic control for adults with diabetes has been set by the American Diabetes Association, whose guidance is followed by health care providers. It states:
- The HbA1c level (a marker of average glucose levels over recent months) should be lowered to 7% to reduce the risk of diabetes complications
- If possible, and as long as hypoglycemia can be avoided, some individuals may be able to target an HbA1c of 6.5%.
Less ambitious HbA1c targets (such as getting below 8%) are appropriate for some patients, including those who have any of the following:9
- History of severe hypoglycemia
- Limited life expectancy
- Advanced diabetes complications
- Extensive coexisting conditions.
Less stringent targets may also be appropriate for people with long-standing diabetes who find targets difficult in spite of disease management strategies.
The 7% HbA1c level informs the equivalent self-monitoring targets that patients can aim for (and again, less ambitious targets are appropriate for some patients):9
- Before meals (preprandial) – 70-130 mg/dL (3.9-7.2 mmol/L)
- After meals (postprandial, 1-2 hours after start of meal) – less than 180 mg/dL (<10.0 mmol/L).
How is a blood glucose monitor used?
A glucose meter electronically reads a small sample of blood on a test strip. The blood is usually drawn by a skin prick at the tip of a finger.
Over 20 types of glucose meter are commercially available, varying in size, the amount of blood needed and electronic memory and analysis features. While some enable graphs to be computed, for many it is up to the user to keep meticulous records including details of times, diet and exercise.
Practical tips for blood glucose monitoring include:
Self-monitoring of type 1 diabetes demands between four and eight finger-prick measurements every day.
- Handle the meter and test strips with clean, dry hands
- Use the test strips specified for the meter and keep these in the original container
- Use a test strip only once and discard
- Strips can be calibrated with the meter for accuracy, and some meters require coding with each new canister of strips
- Check for expiration dates
- Keep in a cool, dry place
- Take the meter to office visits for checks by providers.
Practical steps are also needed in preparation of the skin prick for a blood sample. The skin site should be cleaned with warm, soapy water and dried, or an alcohol pad can be used. Otherwise – if food has been handled recently, for example – false readings can occur.
The lancet sizes vary and can be adjusted to prick the skin and produce the different amounts of blood needed by various meters. Thinner and sharper lancets are typically the most comfortable. Lancets should not be reused after single use.
To reduce pain, the sides of the finger can be used and fingers can be rotated, including any of the five digits instead of the index finger or thumb.
While the most accurate measurements are enabled by the use of the fingertips or outer palm, some meters allow the use of other sites such as the upper arms and thighs.
When should glucose self-monitoring tests be done?
Individual cases of diabetes require different levels of blood glucose monitoring. The frequency of testing can change for an individual as well; the frequency may need to be intensified in the event of changes to medications, stress levels, diet or activity levels.
Examples of the sort of information that can be provided by meter readings include checking oral medicines or long-acting insulins through the use of nighttime fasting blood glucose (FBG) readings, taken at around 3 or 4am.
Test results from before eating can help to guide changes to meals or medicines, and those obtained 1-2 hours following a meal are informative when learning how blood sugar levels are affected by food.
Tests at bedtime also help inform adjustments to diet or medications.
Real-time continuous glucose monitoring
Continuous glucose monitoring overcomes the problem of taking numerous manual daytime readings from skin pricks.
People with type 1 diabetes typically do between four and eight finger-prick measurements each day, and rarely monitor nighttime blood glucose levels.
Such self-monitoring can lead to rapid changes in blood glucose known as excursions, including postprandial hyperglycemia, asymptomatic hypoglycemia and fluctuations overnight.
Real-time continuous glucose monitoring has been shown to be more effective than self blood glucose measurement in reducing HbA1c in type 1 diabetes because it provides detailed information on glucose patterns and trends.
The major factor crucial to the success of the devices is motivation and compliance of the user.
The available continuous monitors – some of which are combined with insulin pumps – consist of an electrochemical sensor placed under the skin and replaced every 3-7 days.