It is well documented that keeping blood glucose levels as close to normal as possible can reduce the risk of the chronic or long-term complications of diabetes, including eye disease (retinopathy), kidney disease (nephropathy), and nerve damage (neuropathy). Accomplishing this task requires knowing what the recommended blood glucose range is, knowing what your blood glucose levels are (by checking on your blood glucose monitor or CGM), and knowing how to bring your levels into range if they are out of goal range.
To help people with diabetes know what they’re aiming for, both the American Diabetes Association and the American College of Endocrinology have published recommended goals for blood glucose control for healthy, nonpregnant adults. There are separate blood glucose goals for pregnant women with diabetes. The goals for healthy adults may need to be modified for certain people, including the elderly.
Blood glucose self-monitoring lets you know what your blood glucose levels are and can often help you and your diabetes team figure how to modify your treatment plan if your levels are out of range. Knowing how to use your meter, therefore, and being able to use it effectively are key to maintaining control of your diabetes.
Blood glucose self-monitoring has both immediate and longer-term applications. In the short term, monitoring can detect high blood glucose (hyperglycemia) and low blood glucose (hypoglycemia), which requires immediate action. (Action is usually recommended when blood glucose is 70 mg/dl or lower.) In the long term, monitoring can reveal patterns in your blood glucose levels that can help you and your diabetes team adjust your treatment plan to improve your blood glucose control.
The number of times you check your blood glucose level each day may depend on your treatment plan and/or your insurance coverage of the supplies needed to check. The times of day you check should be discussed with your diabetes care team. Common times to perform blood glucose monitoring include before meals, after meals, at bedtime, in the middle of the night, and before driving.
Before meals. Premeal blood glucose checks are probably the most commonly recommended checks. The reading taken before breakfast is often referred to as a fasting blood glucose check because it usually comes after 8–12 hours of no food intake. Fasting blood glucose levels provide information about overnight blood glucose control. Monitoring before lunch and dinner provides information about overall diabetes control.
After meals. Your diabetes care team may recommend monitoring approximately 1–2 hours after the start of meals. This result is probably most useful if you check both before and after a meal so that you can compare the two levels. The after-meal result can help you evaluate the effect of any insulin or oral drugs that you take with the intent of controlling after-meal blood glucose levels. These numbers may also help you assess the effects of the types and amount of carbohydrate you eat. You may be advised to check your blood glucose level after meals if your premeal levels are usually within your target range but your HbA1c test results remain above target.
Bedtime. There are at least two good reasons to check your blood glucose level at bedtime. One is to see if it is at a safe level to help prevent you from going low during the night. A bedtime snack may be recommended to keep your blood glucose levels within a safe range overnight. The other is to see how well your treatment plan is working overnight by comparing your bedtime level to your fasting blood glucose level the next morning. Ideally, your blood glucose levels should remain within a fairly close range from the time you go to bed to the time you wake up the next morning. However, this goal may need to be modified to meet individual safety needs.
Middle of the night. Checking your blood glucose level in the middle of the night is particularly useful for insulin users to determine if blood glucose levels are maintained at a reasonably safe level during the night. This is especially true for those who inject intermediate- or long-acting insulin at suppertime or bedtime, as well as for insulin pump users who wish to evaluate their overnight basal rates. In some cases, if fasting or prebreakfast blood glucose levels are too high, it can be the result of “rebounding” from levels that have dropped too low in the middle of the night.
In response to symptoms. If you have signs or symptoms of low blood glucose (hypoglycemia) or high blood glucose (hyperglycemia), it is best to check your blood glucose level to verify your suspicions that you are low or high before taking any action. Symptoms of low blood glucose include weakness, shakiness, sweatiness, hunger, an increase in heart rate, headache, dizziness, and fatigue. However, if you have symptoms of low blood glucose and cannot check, go ahead and treat yourself for low blood glucose to be on the safe side. Treatment involves eating or drinking 15 grams of carbohydrate, the amount found in 1/2 cup of juice or regular soda, 3 glucose tablets, or 5 or 6 pieces of hard candy. If possible, check your blood glucose again after 15 minutes, and treat again if it is still too low. Repeat these steps until your blood glucose level is at least 70 mg/dl.
Prompt treatment of hypoglycemia is important to prevent seizure or loss of consciousness. However, some people who have had high blood glucose for a long time experience one or more of the symptoms of hypoglycemia when their blood glucose levels drop to more normal levels. In this case, raising blood glucose by consuming carbohydrate is not recommended. While it can be hard to resist the urge to eat something in this situation, it is believed that the brain will readjust to more normal blood glucose levels — and a person will no longer experience symptoms of hypoglycemia — if allowed adequate time.
Many people with diabetes can have blood glucose levels that run significantly higher than recommended without having any symptoms that would alert them to elevated blood glucose levels. This is why regular monitoring is useful, and it’s also why it’s important to monitor if you have symptoms of high blood glucose such as frequent urination, dry mouth, thirst, blurred vision, or fatigue, since your blood glucose level may be very high by the time such symptoms appear. Some possible methods of treating high blood glucose include drinking more water, exercising, changing your diet, and changing the amount or timing of your insulin or diabetes drugs. However, there’s no one quick fix for high blood glucose, so you should work out a plan for responding to it with your diabetes care team at your regular appointments before it happens.
Before or after exercise. Blood glucose monitoring can be beneficial in helping you evaluate the effects of exercise and physical activity on your blood glucose control. It is also important to monitor because exercise can cause blood glucose levels to drop, either during or up to 24 hours after activity. For this reason, you should check your blood glucose before you start to exercise, as well as immediately after the activity, to make sure that it is not too low. In addition, if you experience symptoms of hypoglycemia — such as hunger, nervousness, or shakiness — while exercising, stop and check your blood glucose level. If, in any of these situations, your reading is below 70 mg/dl, you should treat for hypoglycemia, wait 15 minutes, and then check your blood glucose again. It is always a good idea to have a source of carbohydrate on hand when you are exercising.
Blood glucose levels that are too high can also make physical activity dangerous. If your blood glucose is over 300 mg/dl, or if you have Type 1 diabetes and it is over 250 mg/dl and you have ketones in your urine, physical activity can make your blood glucose level go even higher. In these situations, exercise is best avoided.
Before driving. It is important to check your blood glucose before driving or operating machinery to avoid any situations that could become dangerous if hypoglycemia should occur.
The American Diabetes Association recommends that the frequency and timing of blood glucose self-monitoring be dictated by your particular needs, with the following considerations:
• Daily monitoring is especially important for people who take insulin, tolbutamide, tolazamide, chlorpropamide (Diabinese), glyburide (brand names DiaBeta, Glynase, and Micronase), glipizide (Glucotrol, Glucotrol XL), glimepiride (Amaryl), combination drugs that contain glyburide, glipizide, or glimepiride (such as Glucovance, Metaglip, Avandaryl, and Duetact), repaglinide (Prandin), or nateglinide (Starlix) to monitor for and prevent asymptomatic hypoglycemia.
• Monitoring three or more times daily is recommended for people with Type 1 diabetes.
• For people with Type 2 diabetes, monitoring sufficient to help them reach blood glucose goals and minimize the risks of both high and low blood glucose episodes is recommended.
• In Type 1 or Type 2 diabetes, monitoring more often is recommended when adding to or modifying therapy.
Other situations in which monitoring closely is recommended include when you are ill, as well as if you are taking a drug or undergoing a treatment for a nondiabetes-related condition that can potentially affect your blood glucose levels.
To get the most accurate results from your meter, you need to be sure you are using proper technique. Here are some basic steps to follow when checking your blood glucose level:
• Insert the test strip into the meter according to manufacturer’s instructions.
• Wash your hands or other area to be lanced with soap and warm water, and dry well.
• Insert a new lancet into the lancing device.
• Press the lancing device firmly against the skin of the area being lanced.
If fingers are being used, stick the side of your finger rather than the center pad, which is more painful and may not produce enough blood.
• Depending on the type of strip you use, place a drop of blood on the correct spot on the test strip, making sure that you completely cover the required area, or hold the strip to the blood drop until enough is drawn in.
Technique will vary somewhat depending on which meter is used — for instance, some meters are preloaded with multiple test strips or feature a built-in lancing device. It is a good idea to bring your blood glucose meter to regular visits with your diabetes care team to review your technique.
Keep in mind that your test strips, in addition to having an expiration date, have a limited period of time — usually several weeks — during which they may be used once their packaging has been opened. Therefore, it is important that you become familiar with the recommendations on the test strip package to establish a time frame for using them. If several strips are packaged together in a vial (or bottle), then all of these strips must either be used or discarded within this time frame.
Because they are sensitive to moisture, light, and extremes of temperature, strips should be stored in their original packaging at all times unless you are in the process of using one. In other words, don’t take strips out of their original container and carry them around, and don’t expose them to temperatures above 86°F or refrigerate them. You may find that using strips that are individually packaged suits you better if you monitor only periodically (as may be the case for a person controlling Type 2 diabetes with meal planning and exercise, or a person with prediabetes). For individually packaged strips, the packaging seal is broken only when the strip is about to be used.
Meters designed to hold multiple test strips eliminate the need for the user to handle individual strips. Some meters use a 10-strip “wheel” cartridge, and one has a 17-strip “drum” cartridge. The cartridge is inserted into the meter according to the manufacturer’s directions and replaced when all the test strips have been used. When it is time to monitor, an individual strip slides out to accept the blood sample; when the test is done, the strip is ejected from the meter. Also available is a disposable meter that comes preloaded with 50 test strips. After the 50th test, the entire meter is simply discarded and replaced.
Like test strips, your meter — whether it is preloaded or uses individual strips — should always be kept away from extremes of temperature. For instance, do not leave your meter in your car, which can become very hot or very cold.
Lancets are considered “used” after one use. Manufacturing companies recommend using a lancet once and then discarding it to prevent infections as well as dulling of the tip once used.
Fingertips have traditionally been used for obtaining blood samples for monitoring, but some meters work with blood samples from other sites, including the fleshy parts of the hand, arm, thigh, or calf. The meters that work with alternative sampling sites are approved by the U.S. Food and Drug Administration (FDA) specifically for this use. Before you buy one of these meters, find out which alternative sites you can use with it, since not all meters are approved for the same sites, and some sites may not be right for you. These meters can usually be used with the fingertips in addition to the alternative sites.
Discuss with your diabetes care team whether alternate-site testing is right for you. If it is, be sure you are instructed in the proper use of your meter with the sites you are planning to use, because the procedure and equipment may be different from what you are used to. For example, when obtaining a blood sample from the arm, you may need to set the lancing device for a deeper puncture to obtain a large enough blood sample. You may also need to rub the area to be lanced or apply heat to increase blood flow before lancing.
It is generally best to use the fingertips when rapid changes in blood glucose level may be occurring. Because blood flow to the finger or palm at the base of the thumb is 3–5 times faster than to the arms and legs, samples from the fingers or palm may show changes in blood glucose level sooner than samples from other areas. For this reason, using blood samples from alternative sites is often recommended only for checks performed either just before or two hours or more after meals, insulin doses, or exercise. If you think that you may be experiencing low blood glucose, or if you have a history of hypoglycemia unawareness (lack of symptoms of hypoglycemia even when blood glucose levels are low), it is best to use your fingers for monitoring.
Record keeping is a vital part of the blood glucose monitoring process. Records can help you identify patterns in your blood glucose levels. For example, knowing that your fasting (prebreakfast) blood glucose level is high, but that your prelunch and presupper values are within the recommended range allows you and your diabetes care team to make changes that target the out-of-range values without upsetting the values that are meeting your goals. Or if your premeal blood glucose values are reasonable but your postmeal values are outside of target range, reviewing carbohydrate intake and/or evaluating need for, or changes in, drug or insulin therapy to target postmeal blood glucose levels may be in order.
Blood glucose readings are key to assessing your overall diabetes plan. Recording your blood glucose monitoring results in a format that allows you to see patterns is important. If you monitor once daily, you can do your checks at different times of day on different days to get a more complete picture of how your blood glucose level typically runs over the course of a day. Meters with memory function can be useful; however, it can be difficult for you or your health-care provider to visualize a pattern just by scrolling back in the memory. Recording values on a designated record sheet can help both you and your diabetes care team to best evaluate patterns.
Some people may prefer to link their meter with a computer software program and print out the records. You can find out if a software program is available for your meter, as well as more about it, by either calling the meter company’s toll-free number or by accessing the company website, which may be printed on the back of the meter and/or in the meter packaging.
If you use your meter often, you will get to know it well. If at any time you feel it is not working, the settings (such as date and time) are incorrect, or the blood glucose numbers you are getting are not what you expect, check it out.
If you are feeling symptoms and the number on your meter doesn’t match, recheck your blood glucose level. Sometimes improper technique or too much or not enough blood on the test strip can lead to inaccurate readings. Double-check your test strips, too. Test strips that have expired or have been exposed to extreme heat or cold often produce inaccurate results.
You should also check to make sure that your meter has been properly calibrated, or that the code number entered into the meter matches the code found on the test strip package. While some newer meters have automatic coding features, others require you to enter a code or insert a special chip or strip every time a new package of test strips is started. Each time you monitor, make sure that the number displayed on the meter matches the code number printed on the package of strips.
If your technique, test strips, and calibration are all OK, try using control solution. Blood glucose meters typically come with a bottle of glucose control solution that can be used to verify that the meter and testing supplies are in working order. To perform a test, apply a drop of solution to a test strip, following any specific instructions that accompany the solution bottle. The control solution is then read by the meter just like a blood glucose sample. The solution contains a “controlled” amount of glucose that, when applied correctly, should read within a certain designated range that is usually printed on the test strip packaging. Before using control solution, check to make sure that it has not passed its expiration date (printed on the bottle) or its discard date (usually the date opened plus three months), which you should mark on the bottle the first time it is opened. If the result of your control solution test does not read within the specified range, you may want to repeat it to verify. If it is still not within the recommended range, then calling the meter company is the next step.
Each meter has a customer service telephone number, which is usually toll-free (or free of charge). This number is most commonly found on the back of the meter and/or in the literature provided in the packaging. Trained personnel are on the phone line to assist with troubleshooting the meter and obtaining a new meter if, in their opinion, your meter does not seem to be in working order.
When you have blood drawn in a laboratory, you may want to check your blood glucose with your meter at the same time and compare the lab’s plasma glucose levels with your meter’s result. (In fact, some labs routinely do this for you when taking blood for an HbA1c test.) Your blood glucose meter is considered accurate if its results fall within 20% of the laboratory results. Also, when comparing results, it is important for you to know whether your meter provides whole-blood or plasma-calibrated results. While older meters provide whole-blood readings, most new meters recalculate their results to indicate only the amount of glucose present in the plasma, or fluid part of the blood. Because glucose is concentrated in the plasma, plasma-calibrated values are generally about 12% higher than whole-blood values. Laboratory tests measure your plasma glucose level, so it is important to make the mathematical adjustment when comparing lab test results to results obtained on a whole-blood meter. If you’re not sure how to do this, ask your doctor or diabetes educator for help.
When it comes time to replace your current meter, think about what features might make monitoring easier for you, and shop around for a new model that has those features. For instance, the size of the meter and the test strip may be a deciding factor. You may want a meter that is very compact and therefore easy to transport; alternatively, finding a meter with a large, easy-to-read display screen may be your priority. Other questions to ask yourself may include:
• Am I interested in basic features only? Or do I want a meter with advanced features, such as graphing of results, ability to add carbohydrate values, and other functions that may be useful day-to-day?
• Do I want a memory feature (where the meter stores results, allowing me to scroll back through and record them at a later date)?
• Is there the option to upload my results to a computer program at home? Can my physician upload results in the office?
• Does my diabetes care team have experience with this meter to assist me with it, if needed?
• What kind of customer support is available and what are the company’s hours of operation?
• Is the meter (and supplies) affordable and/or covered by my medical insurance plan?
Some or all of these questions may apply to you. When choosing a new meter, think about which options are most important and what will help you most on the path toward optimal blood glucose control.