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Patient education: Blood glucose monitoring in diabetes (Beyond the Basics)

Patient education: Blood glucose monitoring in diabetes (Beyond the Basics)
Ruth S Weinstock, MD, PhD
Section Editor:
David M Nathan, MD
Deputy Editor:
Katya Rubinow, MD
Literature review current through: Nov 2022. | This topic last updated: May 20, 2021.

BLOOD GLUCOSE TESTING OVERVIEW — If you have diabetes, you have an important role in your own medical care, and monitoring your blood glucose (sugar) level is a key part of this.

Although diabetes is a chronic condition, it can usually be controlled with lifestyle changes, medication, and self-care measures. The main goal of diabetes treatment is to keep your blood glucose levels in the target range. Checking your blood glucose is one of the best ways to know how well your diabetes treatment plan is working. Blood glucose can be tested with fingersticks and a glucose meter, or with a continuous glucose monitoring (CGM) device, if available. The use of CGM devices has been increasing, especially for people who use an insulin pump or multiple daily insulin injections. (See 'Testing blood glucose with fingersticks and a glucose meter' below and 'Continuous glucose monitoring' below.)

Your health care provider will periodically order a blood test to check your current blood glucose levels and glycated hemoglobin (A1C). The A1C test gives an overall sense of how blood glucose levels are controlled since it measures your average blood glucose level of the past two to three months (table 1). However, in order to most effectively manage your diabetes and adjust your treatment approach as needed, you will also need to check your own blood glucose levels on a daily basis. The exact schedule you will follow depends on several different factors. (See 'Frequency of blood glucose testing' below.)

FREQUENCY OF BLOOD GLUCOSE TESTING — Studies have proven that people with diabetes who maintain normal or near-normal blood glucose levels reduce their risk of diabetes-related complications. (See "Patient education: Preventing complications from diabetes (Beyond the Basics)".)

How often you need to check your blood glucose will depend upon the type of diabetes you have (type 1 or 2), which treatment(s) you use (oral medications, insulin, and/or lifestyle changes), and your treatment goals.

Type 1 diabetes — For people with type 1 diabetes, frequent blood glucose testing is the only way to safely and effectively manage blood glucose levels. People with type 1 diabetes may use blood glucose monitoring (BGM) with fingersticks and a glucose meter, or continuous glucose monitoring ([CGM] if available and affordable). (See 'Continuous glucose monitoring' below and "Patient education: Type 1 diabetes: Overview (Beyond the Basics)".)

Most people not using CGM need to test at least four times per day. If you use an insulin pump, give yourself 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 10 times per day or more. (See "Patient education: Care during pregnancy for patients with type 1 or 2 diabetes (Beyond the Basics)".)

If you don't use CGM, you may want to purchase several blood glucose meters to keep at home, work, school, and/or in a purse or backpack. This way you will be able to access your testing equipment wherever you are, making it easier to keep your blood glucose under control.

Type 2 diabetes — For people with type 2 diabetes, the recommendations for how often to test blood glucose are based upon individual factors such as type of treatment (oral medications, insulin, and/or lifestyle changes), A1C level, risk of hypoglycemia (when blood glucose is too low), and treatment goals.

Blood glucose monitoring is useful for people with type 2 diabetes who take insulin or certain medications that can cause hypoglycemia. It is generally unnecessary in people who manage their diabetes with diet alone or who take medications that do not cause hypoglycemia, especially if they have reached their blood glucose goals. Your health care provider can help you determine how frequently to check your blood glucose based on your situation. (See "Patient education: Type 2 diabetes: Overview (Beyond the Basics)".)


How to check your blood glucose — The following steps include general guidelines for testing blood glucose levels. However, because the instructions can vary between devices, it's best to check the package insert for your glucose meter or talk with your health care provider. It's important to never share monitoring equipment or fingerstick devices, as this could lead to infection.

Wash hands with soap and warm water, then dry.

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 (the exact 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 (picture 1) or alternate site (like the skin of the forearm) (picture 2). Alternate sites are often less painful than the fingertip. However, results from alternate sites are not as accurate as fingertip samples. This should not be a problem if you always use the same site. However, when your blood glucose is rising rapidly (eg, immediately after eating) or falling rapidly (in response to insulin or exercise), it's more accurate to use the fingertip, as testing at alternate sites may give significantly different results in these situations.

If you have difficulty getting a good drop of blood from your fingertip, try rinsing your fingers with warm water and shaking your hand below your waist. This can help get the blood flowing.

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 container designed for sharps (not in household trash).

Blood glucose meters — There is no single blood glucose meter that is better than others. Your health care provider or pharmacist can help you choose a meter based on your preferences as well as other factors like cost, ease of use, and accuracy; it should be one that is approved by either the International Organization for Standardization or the US Food and Drug Administration. Many insurance providers cover the cost of specific meters and/or supplies. Medicare also covers costs of blood glucose monitoring.

Accuracy of home blood glucose monitoring — Blood glucose meters are reasonably accurate. However, there can be some variability between meters, so it is always wise to use caution and common sense. If you get a result that does not fit with how you feel (for example, if it says your blood glucose is very low but you don't have any symptoms), take a second reading or use an alternate method for testing your blood glucose (such as a different meter). Blood glucose meters are least accurate during episodes of low blood glucose. (See "Patient education: Hypoglycemia (low blood glucose) in people with diabetes (Beyond the Basics)".)

The accuracy of blood glucose monitoring can be affected by several factors, including the type of blood glucose strip and meter. Inaccurate readings can be caused by the use of expired strips, improper storage of strips (exposure to high temperature and humidity), inadequate cleansing of your skin, and ingestion of vitamin C and acetaminophen.

It's a good idea to check the accuracy of your blood glucose meter occasionally by bringing it with you when you have an appointment to get blood testing. This way, you use your home monitor to check your blood glucose at the same time that blood is drawn and compare the results. If the results differ by more than 15 percent, there may be a problem with your meter or other equipment; your provider can help you figure out what's going on and how to correct the problem.

Help for people with vision impairment — People with vision impairment (a common complication of diabetes) sometimes have difficulty using glucose meters. Meters with large screens and "talking" meters are available. If you have impaired vision, you can get help from the American Association of Diabetes Care and Education Specialists (ADCES) at (800) 338-3633.

CONTINUOUS GLUCOSE MONITORING — Continuous glucose monitoring (CGM) is a way to monitor your blood glucose levels every 5 to 15 minutes, 24 hours a day. Because of reliability issues, warm-up periods, and the need to calibrate some of the devices, CGM does not eliminate the need for at least occasional fingersticks.

CGM systems use a glucose sensor to measure the level of glucose in the fluid under the skin. The sensor is attached to a transmitter placed on your skin, which is held in place with a sticky patch (figure 1). It wirelessly transmits results to a small recording device (no larger than a cell phone) or to a smartphone or other smart device. In some cases, it transmits the information directly to an insulin pump (figure 2). You can attach the recording device to your clothing, carry in a purse or bag, or place it near you (eg, on a bedside table).

If you use a CGM system, you will need to remove the sensor and replace it on a different part of your body approximately once every 7 to 14 days. Different CGM systems are available; one implantable sensor can last up to 90 days, but needs to be inserted and removed by a physician, nurse practitioner, or physician assistant.

CGM systems are most often used by people with type 1 diabetes who give themselves multiple daily insulin injections or use an insulin pump. Devices that combine an insulin pump with a CGM system are also available (see "Patient education: Type 1 diabetes: Insulin treatment (Beyond the Basics)"). Many experts think that CGM may be most useful in people who have frequent episodes of low blood glucose, episodes of low blood glucose during the night ("nocturnal hypoglycemia"), large fluctuations in their blood glucose levels, and/or difficulty recognizing when they have low blood glucose.

Use of CGM is also appropriate for people with type 2 diabetes who need multiple daily insulin injections, particularly those with frequent episodes of low blood glucose or difficulty recognizing when they have low blood glucose. Periodic use of CGM can also help you and your doctor determine when the blood glucose is low and high and how to adjust your insulin dose (or food intake) to prevent it.

Advantages — There is evidence that people with type 1 diabetes who use a CGM system consistently and reliably (rather than the fingerstick method) have modestly better-controlled blood glucose levels.

The "real-time" CGM devices automatically display your blood glucose level every five minutes, using numbers, graphics, and arrows so you can easily tell if your level is increasing, decreasing, or stable. The receiver (recording device) can also be set to trigger an alarm if your blood glucose level gets above or below a preset level, which can be especially helpful for people who cannot feel when they have low blood glucose (also known as "hypoglycemia unawareness"). Some CGM systems permit real-time "sharing" of your CGM readings with others (eg, family members or caregivers). The less expensive "intermittently scanned" or "flash" CGM devices record your blood glucose every 15 minutes and display glucose trends, but to view these results you have to scan the sensor/transmitter with the reader/receiver. Some, but not all, of these intermittently scanning CGM devices are able to alert you of low or high blood glucose readings.

You can download blood glucose results from the CGM system to your computer, tablet, or smartphone, allowing you to see blood glucose trends over time. If you take insulin, your health care provider can help you figure out how to use this information to adjust your insulin dose if needed.

Drawbacks — The continuous glucose sensors may show lower glucose values than blood glucose meters, especially when blood glucose levels are rapidly rising. CGM systems also tend to be less accurate when blood glucose is low (<40 mg/dL or 2.2 mmol/L) and therefore may not be able to reliably indicate when this is happening. With many CGM systems, you will still need to check your blood glucose using a fingerstick at least occasionally, to calibrate some of the devices and/or to confirm a blood glucose reading before insulin dosing.

In addition, the costs associated with CGMs are greater than those of traditional glucose meters. Not all continuous glucose meters and supplies are covered by commercial health insurance companies.


Blood glucose testing — The results of blood glucose testing tell you how well your diabetes treatments are working. However, blood glucose results can be affected by different things, including your level of physical activity, what you eat, stress, and medications (including insulin and oral diabetes medications). To fully understand what your blood glucose levels mean, it is important to consider all of these factors.

When keeping track of your results, you should include the time and date, blood glucose result, and the medication and dose you are taking. Additional notes about what you ate, whether you exercised, and any difficulties with illness or stress can also be helpful but are not generally required every day. You should review this information regularly with your health care provider to understand what your results mean and whether you need to make any changes to better manage your blood glucose.

Need for urine testing — If you have type 1 diabetes, your health care provider will talk to you about checking your urine for ketones. You will need to do this if your blood glucose level gets above 250 to 300 mg/dL (13.9 to 16.7 mmol/L), during periods of illness or stress, or if you have symptoms of a problems called 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 is a condition that occurs when high levels of ketones are present in the body; it 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 health care 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. Meters that measure ketone levels in the blood are also available, but due to their cost, urine testing is more widely used.

ADJUSTING TREATMENT — Home blood glucose monitoring or continuous glucose monitoring (CGM) provides useful information and is an important part of managing your diabetes. If you use insulin, your blood glucose results will help guide you in choosing the appropriate doses from meal to meal. When you first start treatment for diabetes, you will need to work with your health care 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.

WHERE TO GET MORE INFORMATION — Your health care 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 website ( Related topics for patients, as well as selected articles written for health care 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 education: Type 2 diabetes (The Basics)
Patient education: Using insulin (The Basics)
Patient education: Treatment for type 2 diabetes (The Basics)
Patient education: Low blood sugar in people with diabetes (The Basics)
Patient education: Care during pregnancy for people with type 1 or type 2 diabetes (The Basics)
Patient education: My child has diabetes: How will we manage? (The Basics)
Patient education: Controlling blood sugar in children with diabetes (The Basics)
Patient education: Managing diabetes in school (The Basics)
Patient education: Hemoglobin A1C tests (The Basics)
Patient education: Giving your child insulin (The Basics)
Patient education: Checking your child's blood sugar level (The Basics)
Patient education: Diabetic ketoacidosis (The Basics)
Patient education: Hyperosmolar hyperglycemic state (The Basics)
Patient education: 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 education: Type 1 diabetes: Overview (Beyond the Basics)
Patient education: Care during pregnancy for patients with type 1 or 2 diabetes (Beyond the Basics)
Patient education: Type 2 diabetes: 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.

Glucose monitoring in the ambulatory management of nonpregnant adults with diabetes mellitus
Measurements of glycemia in diabetes mellitus
Overview of the 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)

(800)-DIABETES (800-342-2383)


Hormone Health Network

(, available in English and Spanish)


This generalized information is a limited summary of diagnosis, treatment, and/or medication information. It is not meant to be comprehensive and should be used as a tool to help the user understand and/or assess potential diagnostic and treatment options. It does NOT include all information about conditions, treatments, medications, side effects, or risks that may apply to a specific patient. It is not intended to be medical advice or a substitute for the medical advice, diagnosis, or treatment of a health care provider based on the health care provider's examination and assessment of a patient's specific and unique circumstances. Patients must speak with a health care provider for complete information about their health, medical questions, and treatment options, including any risks or benefits regarding use of medications. This information does not endorse any treatments or medications as safe, effective, or approved for treating a specific patient. UpToDate, Inc. and its affiliates disclaim any warranty or liability relating to this information or the use thereof. The use of this information is governed by the Terms of Use, available at ©2023 UpToDate, Inc. and its affiliates and/or licensors. All rights reserved.
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