Patient information: Self-blood glucose monitoring in diabetes mellitus (Beyond the Basics)
- David K McCulloch, MD
David K McCulloch, MD
- Clinical Professor of Medicine
- University of Washington
BLOOD SUGAR TESTING OVERVIEW
If you have diabetes, you have an important role in your own medical care, and testing your blood glucose (also called blood sugar) is an opportunity for you to take control of your health.
Although diabetes is a chronic condition, it can usually be controlled with lifestyle changes and medication. The main goal of treatment is to keep blood sugar levels in the normal or near-normal range. Checking your blood sugar is one of the best ways to know how well your diabetes treatment plan is working. Continuous glucose monitors have also become popular, especially for people who use an insulin pump. (See 'Continuous glucose monitoring' below.)
A healthcare provider will periodically order a laboratory blood test to determine your blood sugar levels and hemoglobin A1c (A1C). This test gives an overall sense of how blood sugar levels are controlled since it indicates your average blood sugar level of the past two to three months (table 1). However, fine-tuning of blood sugar levels and treatment also requires that you monitor your own blood sugar levels on a day-to-day basis.
Self-blood glucose monitoring allows you to know your blood glucose level at any time and helps prevent the consequences of very high or very low blood sugar. Monitoring also enables tighter blood sugar control, which decreases the long-term risks of diabetic complications.
HOW TO PERFORM BLOOD SUGAR TESTING
The following steps include general guidelines for testing blood sugar levels; you should get specific details for your blood glucose monitors from the package insert or your healthcare provider. Never share blood glucose monitoring equipment or fingerstick lancing devices. Sharing of this equipment could result in transmission of infection, such as hepatitis B.
●Wash hands with soap and warm water. Dry hands.
●Prepare the lancing device by inserting a fresh lancet. Lancets that are used more than once are not as sharp as a new lancet, and can cause more pain and injury to the skin.
●Prepare the blood glucose meter and test strip (instructions for this depend upon the type of glucose meter used).
●Use the lancing device to obtain a small drop of blood from your fingertip or alternate site (like the skin of the forearm) (picture 1). Alternate sites are often less painful than the fingertip. However, results from alternate sites are not as accurate as fingertip samples when the blood glucose is rising or falling rapidly (picture 2).
If you have difficulty getting a good drop of blood from the fingertip, try rinsing your fingers with warm water, shaking the hand below the waist, or squeezing ("milking") the fingertip.
●Apply the blood drop to the test strip in the blood glucose meter. The results will be displayed on the meter after several seconds.
●Dispose of the used lancet in a puncture-resistant sharps container (not in household trash).
FREQUENCY OF BLOOD SUGAR TESTING
Studies have proven that people with type 1 and 2 diabetes who maintain normal or near normal blood sugar levels have a lower risk of diabetes-related complications than those who have high blood sugar levels. How frequently you test will depend upon the type of diabetes you have (1 or 2) and which treatment(s) you use (insulin versus oral medications or lifestyle changes).
Type 1 diabetes — For people with type 1 diabetes, frequent testing is the only way to safely and effectively manage blood sugar levels. (See "Patient information: Diabetes mellitus type 1: Overview (Beyond the Basics)".)
Most people need to test at least four times per day. If you use an insulin pump, give three or more insulin injections per day, or are a woman with type 1 diabetes who is pregnant, you may need to test as many as seven times per day or more. (See "Patient information: Care during pregnancy for women with type 1 or 2 diabetes mellitus (Beyond the Basics)".)
People who test frequently, especially those using intensive insulin therapy, may consider purchasing several blood glucose monitors to keep at home, work, school, or in a purse or backpack. This allows easier access to testing equipment, which can increase testing frequency and therefore improve blood sugar control.
Type 2 diabetes — Blood sugar monitoring is also important for people with type 2 diabetes. The recommendations for how often you should test are based upon individual factors such as type of treatment (diet versus oral medication versus insulin), level of hemoglobin A1c (A1C), and treatment goals. A healthcare provider can help you determine how frequently to test. (See "Patient information: Diabetes mellitus type 2: Overview (Beyond the Basics)".)
INTERPRETING BLOOD SUGAR RESULTS
Blood sugar testing — The results of blood sugar testing tell you if your diabetes treatments are on target. However, blood sugar results can be affected by activity levels, foods eaten, and medications (including insulin and oral diabetes medications). To interpret results, it is important to consider all of these factors.
You should review your blood sugar results regularly with a healthcare provider. The record should include the time and date, blood glucose result, and dose of medication used; additional notes about what you ate, exercise, and difficulties with illness or stress can also be helpful but are not generally required every day.
Need for urine testing — People with type 1 diabetes should perform urine testing for ketones if the blood sugar level is above 240 mg/dL (13.3 mmol/L), during periods of illness or stress, or if you have symptoms of ketoacidosis, such as nausea, vomiting, and abdominal pain.
Ketones are acids that are formed when the body does not have enough insulin to get glucose into the cells, causing the body to break down fat for energy. Ketones can also develop during illness, if an inadequate amount of glucose is available (due to skipped meals or vomiting). Ketoacidosis occurs when high levels of ketones are present and can lead to serious complications such as diabetic coma.
Urine ketone testing is done with a dipstick, available in pharmacies without a prescription. If you have moderate to large ketones, you should call your healthcare provider immediately to determine the best treatment. You may need to take an additional dose of insulin, or your provider may instruct you to go to the nearest emergency room.
Home blood sugar monitoring can provide useful and motivating information. For people who are treated with insulin, the results will help guide you to choose the appropriate doses from meal to meal. In the beginning of your treatment, you will need to consult with your healthcare provider as you learn to make adjustments in treatment. However, with time and experience, most people are able to learn how to make adjustments on their own.
ACCURACY OF HOME BLOOD SUGAR MONITORING
The accuracy of a blood glucose monitor can be affected by several factors, including the type of blood glucose strip and monitor.
Check the accuracy of a blood glucose monitor occasionally by bringing it to visits with a healthcare provider when blood work is done; use your home monitor to check your blood sugar at the same time that blood is drawn.
When comparing glucose monitor results with those from a laboratory, there should be no more than a 15 percent difference; larger differences may indicate a problem with your monitor, blood glucose strips, or your monitoring technique.
Blood glucose meters — Blood glucose meters are reasonably accurate. However, there can be some variability from one unit to the next, so it is always wise to exercise caution and common sense when using the readings from these machines. As an example, if a reading does not fit with your symptoms (or lack of symptoms), take a second reading or use an alternate method for testing your blood sugar (such as a different meter). Blood glucose meters are least accurate during episodes of low blood sugar.
Alternate site testing — Blood sugar results can be less accurate if you test at places other than the fingertips (eg, arm, hand, leg). This should not be a problem if you always use one site. However, when the blood sugar is rising rapidly (eg, immediately after eating) or falling rapidly (in response to insulin or exercise), testing at alternate sites may give significantly different results than a fingerstick reading. In these situations, fingertip testing is preferred.
Help for people with vision impairment — People with vision impairment sometimes have difficulty using glucose meters. Meters with large screens and "talking" meters are available. People with impaired vision can get assistance from the American Association of Diabetes Educators (AADE) at (800) 338-3633.
SELECTING A BLOOD GLUCOSE MONITOR
There is no single blood glucose monitor that is better than others. A number of factors should be considered when choosing a monitor:
●Expense – Special offers, rebates, and trade-ins are almost always available on blood glucose monitors, making them affordable for most people. Also check the cost of the supplies that go along with a monitor, including test strips. Over time, supplies will be more costly than the monitor. Many insurance carriers cover the cost of the monitor and/or supplies. Medicare now covers all of the costs of blood glucose monitoring.
●Ease of use – Some monitors are easier to use than others. Some require a tiny sample of blood, meaning that a smaller and less painful finger stick is possible. Meters vary in how quickly they give the result (some in as little as five seconds). When possible, check with a pharmacist, diabetes nurse, or other healthcare provider for a recommendation.
●Accuracy – Newer meters typically provide the most reliable results.
●Sophistication – Some meters allow you to enter events (like eating or exercising) and come with software programs that allow you to download data to a computer. This is most helpful for people who test frequently and use intensive insulin treatment.
CONTINUOUS GLUCOSE MONITORING
Continuous glucose monitoring systems (CGMS) use a glucose sensor (contained in a small needle) to determine the level of glucose in the fluid under the skin. The sensor is attached to the skin with a sticky patch, and it wirelessly transmits results to a small recording device (the size of a pager or cell phone), which you wear on your clothing, carry in a purse or bag, or place near you (eg, a bedside table). The monitor updates and displays your blood sugar level every few minutes.
You must remove and replace the sensor in a different place on your body approximately once per week. In addition, you must continue to perform finger stick blood sugar testing several times daily to ensure that the continuous monitor is correctly calibrated.
Currently, continuous blood glucose monitors are recommended only for people with type 1 diabetes who use intensive insulin therapy, often with an insulin pump. A combined insulin pump and continuous glucose monitor is also available. Many experts think that continuous glucose monitoring may be most useful in people who have difficulty recognizing when they have low blood sugar.
Advantages — The continuous glucose monitor displays your blood sugar level every few minutes, allowing you to see if the level is increasing, decreasing, or is stable. The receiver can also be set to alarm if your blood sugar level is above or below a pre-set level, which can be especially helpful for people who cannot feel when they have low blood glucose (so called hypoglycemia unawareness).
You can download blood sugar results from the continuous monitor to your computer, allowing you to see blood sugar trends over time. You can use this information to determine if you need to adjust your insulin dose.
Drawbacks — The continuous glucose sensors currently available are not as accurate as most blood glucose monitors, especially when blood glucose levels are rapidly rising. In one study, over 70 percent of the blood and continuous glucose values differed by 10 percent or more, and 7 percent of the readings differed by over 50 percent . The CGMS tends to be less accurate when the blood sugar is low (<70 mg/dL or 3.9 mmol/L) and therefore may not be able to reliably indicate when you are low.
Thus, most experts do not recommend continuous glucose monitoring alone for information about your blood glucose levels. It is important to do several fingersticks daily to calibrate the CGMS device and to verify that the sensor readings are accurate.
In addition, the costs associated with continuous glucose monitors are much greater than those of traditional glucose monitors. Not all continuous glucose meters and supplies are covered by commercial health insurance companies.
WHERE TO GET MORE INFORMATION
Your healthcare provider is the best source of information for questions and concerns related to your medical problem.
This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.
Patient level information — UpToDate offers two types of patient education materials.
The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.
Patient information: Type 2 diabetes (The Basics)
Patient information: Using insulin (The Basics)
Patient information: Treatment for type 2 diabetes (The Basics)
Patient information: Low blood sugar in people with diabetes (The Basics)
Patient information: Care during pregnancy for women with type 1 or type 2 diabetes (The Basics)
Patient information: My child has diabetes: How will we manage? (The Basics)
Patient information: Keeping your child’s blood sugar under control (The Basics)
Patient information: Managing diabetes in school (The Basics)
Patient information: Giving your child insulin (The Basics)
Patient information: Checking your child’s blood sugar level (The Basics)
Patient information: Diabetic ketoacidosis (The Basics)
Patient information: Hyperosmolar nonketotic coma (The Basics)
Patient information: Diabetes and infections (The Basics)
Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.
Patient information: Diabetes mellitus type 1: Overview (Beyond the Basics)
Patient information: Care during pregnancy for women with type 1 or 2 diabetes mellitus (Beyond the Basics)
Patient information: Diabetes mellitus type 2: Overview (Beyond the Basics)
Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.
Blood glucose self-monitoring in management of adults with diabetes mellitus
Estimation of blood glucose control in diabetes mellitus
Management of type 1 diabetes mellitus in children and adolescents
Treatment of type 2 diabetes mellitus in the older patient
The following organizations also provide reliable health information.
●National Library of Medicine
●National Institute of Diabetes and Digestive and Kidney Diseases
●American Diabetes Association (ADA)
●Hormone Health Network
(www.hormone.org, available in English and Spanish)
- Metzger M, Leibowitz G, Wainstein J, et al. Reproducibility of glucose measurements using the glucose sensor. Diabetes Care 2002; 25:1185.
- Faas A, Schellevis FG, Van Eijk JT. The efficacy of self-monitoring of blood glucose in NIDDM subjects. A criteria-based literature review. Diabetes Care 1997; 20:1482.
- Nettles A. User error in blood glucose monitoring. The National Steering Committee for Quality Assurance Report. Diabetes Care 1993; 16:946.
- Self-monitoring of blood glucose. American Diabetes Association. Diabetes Care 1994; 17:81.
- Most RS, Gross AM, Davidson PC, Richardson P. The accuracy of glucose monitoring by diabetic individuals in their home setting. Diabetes Educ 1986; 12:24.
All topics are updated as new information becomes available. Our peer review process typically takes one to six weeks depending on the issue.