Self-Monitoring of Blood Glucose

Self-monitoring of blood glucose (SMBG) is used to measure blood sugar (glucose). Glucose is blood sugar that your body uses as a source of energy. Unless you have diabetes, your body regulates the amount of glucose in your blood. People with diabetes have poorly-controlled blood glucose. It’s important to your health to control your blood glucose. Keeping your glucose level close to normal helps prevent or delay some diabetes problems, such as eye disease, kidney disease, and nerve damage. One thing that can help you control your glucose level is to keep track of it through testing.

Other names

• Home Blood Glucose Testing
• SMBG

Who should test their blood glucose?

You should test your glucose if you have diabetes and you need to monitor your blood sugar (glucose) levels. Blood glucose testing can help you understand how food, physical activity, and diabetes medicine affect your glucose levels. Testing can help you make day-to-day choices about how to balance these things. If you have type 2 diabetes your GP or diabetes care team will need to take a reading of your long term blood glucose level about every 2-6 months. This shows how stable your glucose levels have been in the recent past and how well your treatment plan is working.

Getting started

Ask your health care team to help you set a goal for your glucose range and show you how to record your glucose readings in a logbook or record sheet. If you need a daily logbook, ask your health care provider for one. Or you can make copies of the records page. A sample log sheet is filled out to show you how to use each.

Be sure to write down each glucose reading and the date and time you took it. When you review your records, you can see a pattern of your recent glucose control. Keeping track of your glucose on a day-to-day basis is one of the best ways you can take charge of your diabetes.

Types of Blood Glucose Tests

Before you self-monitor your blood glucose, you must read and understand the instructions for your meter. There are two common tests for blood sugar. They can help you and your doctor check how well your blood sugar is under control.

• Finger Stick
  One test is a finger stick that you can do at home. Your health care team can show you how to do the test yourself. This test is done one or more times a day. It can be done first thing in the morning before you eat (fasting) or at other times of the day. Your doctor or nurse will use this information when you go for a checkup. This test tells what your blood sugar level is at that moment in time. The target is usually 100 to 120. The fasting target is usually 80 to 120. After a meal, the target is usually less than 180.

In general, you prick your finger with a a finger prick called a lancet to get a drop of blood. Place the blood on a disposable "test strip" that is coated with chemicals that react with glucose. Then place the test strip in your electronic meter. Some meters measure the amount of electricity that passes through the test strip. Others measure how much light reflects from it. In the U.S. meters report results in milligrams of glucose per deciliter of blood or mg/dl.

• HbA1c Test

The other test is a blood test called hemoglobin A1c (HEE-muh-glo-bin AY-one-see). It is often called just A1c. This test is done at your doctor's office or a lab a few times a year. The A1c shows the average blood sugar level over the past 2 to 3 months. It tells how well blood sugar is managed. Usually the goal is for your A1c to be below 7. This means that your finger-stick blood sugars have been in good range over the past 2 to 3 months.

You can get information about your meter and test strips from several different sources including the toll free number in the user manual or the manufacturer's web site. If you have an urgent problem, always contact your healthcare provider or a local emergency room for advice.

How often should you test your glucose?

Follow your doctor's recommendations about how often you test your glucose. You may need to test yourself several times each day to determine adjustments in your treatment. Many people with diabetes test their glucose 2 to 4 times a day.

How are glucose levels measured?

In home testing, blood glucose levels are usually measured in terms of how many millimoles of glucose there is in a litre of blood. A millimole is a measurement that is used to define the concentration of glucose in your blood. The measurement is expressed as millimoles per litre, or mmol/l, for short.

Blood glucose levels vary from person to person and the amount of glucose in your blood will also change throughout the day. Therefore, there is no such thing as an ‘ideal' blood glucose level.

However, a normal blood glucose level is between 4.0-6.0 mmol/l before meals (preprandial), and less than 10.0 mmol/l two hours after meals (postprandial). Your diabetes care team will be able to discuss your blood glucose level in more detail with you.

What should your glucose levels be?

Your fasting blood glucose level (after not eating for 8-10 hours) should be lower than 126 mg/dL. Your blood glucose level immediately after eating should be lower than 200 mg/dL.

How do you choose a Glucose Meter?

You can purchase more than 25 different types of meters. They differ in several ways including

• amount of blood needed for each test
• how easy it is to use
• pain associated with using the product
• accuracy
• testing speed
• overall size
• ability to store test results in memory
• cost of the meter
• cost of the test strips used
• doctor's recommendation
• technical support provided by the manufacturer
• special features such as automatic timing, error codes, large display screen, or spoken instructions or results

Talk to your health care practitioner about glucose meters and how to use them.

How do you compare your home test glucose values with the laboratory values?

Most home blood glucose meters in the U.S. measure glucose in whole blood. Most lab tests, in contrast, measure glucose in plasma. Plasma is blood without the cells. A lab test of your blood glucose will be about 10-15% higher than the value given by your meter. Look at the instructions for your meter to find out if it gives its results as "whole blood" or "plasma equivalent." Many meters now sold give values that are "plasma equivalent," which means they can be compared more directly to lab test values.

Should you use generic or "third party" test strips?

You may choose test strips that are made by a different company than the one that made meter. Sometimes, generic test strips are cheaper. If you choose generic test strips

• make sure the generic strips will work with your meter. Check the label of the test strips to make sure they will work with the make and model of your meter. Just because the generic test strip looks like it will work does not mean that it will work.
• watch for inconsistent results. If you get poor results, try strips made or recommended by the maker of your meter until you again get consistent results.

How can you check your meter's performance?

There are three ways to make sure your meter works properly:

1. Use liquid control solution
   • every time you open a new container of test strips
   • occasionally as you use the container of test strips
   • whenever you get unusual results You test a drop of these solutions just like you test a drop of your blood. The value you get should match that written on the liquid control solution bottle.
2. Use electronic checks. Every time you turn on your meter, it does an electronic check. If it detects a problem it will give you an error code. Look in your owner's manual to see what the error codes mean and how to fix the problem.
3. Compare your meter with a laboratory meter. Take your meter with you to your next appointment with your health care provider. Ask your provider to watch your technique to make sure you are using the meter correctly. Ask your healthcare provider have your blood tested with a routine laboratory method. If the values you obtain on your glucose meter match the laboratory values, then your meter is working well and you are using good technique.

What should you do if your meter malfunctions?

If your meter malfunctions, you should tell your health care professional and the company that made your meter and strips.

Can you test blood glucose from sites other than your fingers?

Some new meters allow you to test blood from the base of your thumb, upper arm, forearm, thigh, or calf. If your glucose changes rapidly, these other sites may not give you accurate results. You should probably use your fingers to get your blood for testing if any of the following applies

• you have just taken insulin
• you think your blood sugar is low
• you are not aware of symptoms when you become hypoglycemic
• the site results do not agree with the way you feel
• you have just eaten
• you have just exercised
• you are ill
• you are under stress

How accurate is the blood glucose test?

The accuracy of this test depends on many factors including:

• the quality of your meter.
• the quality of your test strips.
• how well you do the test.
• your hematocrit (the amount of red blood cells in the blood). If you have a high hematocrit, you may test low for blood glucose. Or, if you have a low hematocrit, you may test high for glucose. If you know your hematocrit is low or high, discuss with your health care provider how it may affect your glucose testing.
• interfering substances (some substances, such as Vitamin C and uric acid, may interfere with your glucose testing). Check the package insert for your meter and test strips to find out what substances may affect the testing accuracy.
• Altitude, temperature, and humidity (high altitude, low and high temperatures, and humidity can cause unpredictable effects on glucose results). Check the meter and test strip package inserts for more information. Store and handle the meter and strips according to instructions.

Useful Links

• Useful Tips to Increase Accuracy and Reduce Errors in Test Results from Glucose Meters
• Common Problems with the Use of Glucose Meters
• Getting Up to Date on Glucose Meters
• National Diabetes Information Clearinghouse (National Institutes of Health)
• Lab Tests Online: Glucose Exit Disclaimer

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