Patient education: Glucose monitoring in diabetes (Beyond the Basics)

GLUCOSE TESTING OVERVIEW — 

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

Although diabetes is a chronic condition, it can usually be managed with lifestyle changes, medication, and self-care measures. The main goal of diabetes treatment is to keep your glucose levels in the goal range. Checking your glucose is one of the best ways to know how well your diabetes treatment plan is working. 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 insulin. (See 'Blood glucose monitoring (BGM)' below and 'Continuous glucose monitoring' below.)

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

METHODS OF GLUCOSE MONITORING — 

Glucose monitoring can be done in two ways, blood glucose monitoring (BGM) and continuous glucose monitoring (CGM).

Blood glucose monitoring — BGM requires fingersticks to get small samples of blood for testing; you can also use alternate sites such as the forearm. The glucose level in the blood sample is measured with a glucose meter. The detailed steps for checking blood glucose through BGM are described below. (See 'How to check your blood glucose' below.)

Continuous glucose monitoring — CGM systems use a 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 it 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 15 days. Different CGM systems are available; one implantable sensor can last up to 365 days, but it needs to be inserted with a minor surgical procedure and removed by a health care provider.

Prescription CGMs can be programmed to alert you if your glucose is below a certain preset level. They can also alert you if your glucose level is high. Your health care provider can talk to you about how to program these alerts and what your goal blood glucose level should be. It is also possible to buy CGMs over-the-counter (without a prescription); however, these do not alert for high or low glucose readings and should not be used by people who take insulin.

FREQUENCY OF 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. Checking your glucose levels can play an important role in achieving your glucose goals and reducing the risk of complications. (See "Patient education: Preventing complications from diabetes (Beyond the Basics)".)

How often you need to check your glucose will depend on:

●The type of diabetes you have (type 1 or 2)

●Which treatment(s) you use (oral medications, insulin, non-insulin injectable medications, and/or lifestyle changes)

●Your treatment goals

Type 1 diabetes — For people with type 1 diabetes, frequent 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). In people with type 1 diabetes, CGM is recommended if available and affordable. (See 'Methods of glucose monitoring' above and 'Continuous glucose monitoring' below and "Patient education: Type 1 diabetes: Overview (Beyond the Basics)".)

Most people with type 1 diabetes who use BGM alone need to check their blood glucose level at least four times every day. If you use an insulin pump, give yourself three or more insulin injections per day, or are currently pregnant, you may need to test as many as 10 times a day. (See "Patient education: Care during pregnancy for patients with type 1 or 2 diabetes (Beyond the Basics)".)

If you use BGM alone, 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 manage your blood glucose.

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

Glucose monitoring is particularly useful for people with type 2 diabetes who take insulin or certain medications that can cause hypoglycemia. It is often 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 glucose and/or A1C goals. Your health care provider can help you determine how frequently to check your glucose based on your situation. In general, regardless of which medications you take, if you feel ill or develop symptoms of high or low blood sugar, you should check your glucose. Most people with type 2 diabetes who perform glucose monitoring use BGM. For people taking insulin, CGM can be considered if available and affordable. (See 'Who should use CGM?' below and "Patient education: Type 2 diabetes: Overview (Beyond the Basics)".)

BLOOD GLUCOSE MONITORING (BGM)

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.

●Prepare the lancing device by inserting a fresh lancet (needle). 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 on the type of glucose meter used.

●Use the lancing device to obtain a small drop of blood from your fingertip (figure 3) or alternate site (like the skin of the forearm) (picture 1). Alternate sites are often less painful than the fingertip. However, in some settings, results from alternate sites may be less accurate, and fingertip samples are preferred. For example, 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. Check with your health care provider if you are not sure which site you should use.

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 (FDA). Many insurance providers cover the cost of specific meters and/or supplies. Medicare also covers costs of BGM.

Accuracy of home BGM — 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 BGM 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 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 are described in detail above (see 'Continuous glucose monitoring' above).

Who should use CGM? — You might be able to use continuous glucose monitoring (CGM) if you use insulin therapy and need to adjust insulin doses based on your glucose levels.

CGM use may be most helpful in people who have one or more of the following:

●Frequent episodes of hypoglycemia (low blood glucose)

●Episodes of low blood glucose during the night ("nocturnal hypoglycemia")

●Large fluctuations in blood glucose levels

●Difficulty recognizing when they have low blood glucose

CGM systems are most often used by people using multiple daily insulin injections or an insulin pump. Periodic use of CGM can also help you and your health care provider determine when your glucose is low or high and how to adjust your medication doses or food intake to prevent these fluctuations.

Devices that combine an insulin pump with a CGM system are also available. (See "Patient education: Type 1 diabetes: Insulin treatment (Beyond the Basics)".)

For people with type 2 diabetes not using insulin and who do not experience hypoglycemia, less expensive CGMs are available. They can help you see how food and activity affect your glucose levels. These CGMs do not require a prescription and are not covered by insurance. Importantly, these over-the-counter devices cannot be programmed to alert you if your blood glucose gets too low or too high; for this reason, they are not recommended for people who take insulin.

Advantages — There is evidence that people with type 1 diabetes who use a CGM system consistently and reliably (rather than blood glucose monitoring [BGM]) have better-managed blood glucose levels.

The "real-time" CGM devices automatically display your glucose level every five minutes, using numbers, graphics, and arrows so you can easily tell if your level is increasing, decreasing, or stable (figure 4). The receiver (recording device) can also be set to trigger an alarm if your 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 "impaired awareness of hypoglycemia" or "hypoglycemia unawareness"). Most 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 glucose every 15 minutes and display glucose trends, but to view these results you have to scan the sensor/transmitter with the reader/receiver (figure 1). Some, but not all, of these intermittently scanning CGM devices are able to alert you of low or high glucose readings.

You can download glucose results from the CGM system to your computer, tablet, or smartphone, allowing you to see glucose trends over time. Glucose readings can also be shared with health care providers using cloud-based systems. 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 — CGM systems may show lower glucose values than blood glucose meters, especially when blood glucose levels are rapidly rising. They may also show higher levels when glucose levels are falling rapidly. CGM systems tend to be less accurate when blood glucose is very low (<40 mg/dL or 2.2 mmol/L) and therefore may not be able to reliably indicate when this is happening. You will still need to check your blood glucose using a glucose meter at least occasionally, to calibrate some of the devices and/or to confirm a glucose reading before insulin dosing or treating a low blood sugar.

Glucose readings from CGM may be inaccurate if you take hydroxyurea, high-dose acetaminophen (more than 1000 mg every six hours), or high-dose vitamin C (1000 mg or more a day).

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

INTERPRETING GLUCOSE MEASUREMENTS

Glucose testing — The results of glucose testing with blood glucose monitoring (BGM) or continuous glucose monitoring (CGM) tell you how well your diabetes treatments are working from hour to hour and day to day. Glucose results can be affected by different things, including your level of physical activity, what you eat, stress, and medications (including insulin, non-insulin injectable medications, and oral diabetes medications). To fully understand what your 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, 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 glucose levels.

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 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 problem called ketoacidosis (such as nausea, vomiting, and abdominal pain). Ketoacidosis can also develop at lower glucose levels if you are taking a medication called a sodium-glucose cotransporter 2 (SGLT2) inhibitor. If you take this kind of medication, discuss ketone testing with your health care provider.

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 and are more accurate, but due to their cost, urine testing is more widely used.

ADJUSTING TREATMENT — 

Checking your glucose (either with blood glucose monitoring [BGM] or continuous glucose monitoring [CGM]) provides useful information and is an important part of managing your diabetes. If you use insulin, your 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 adjust your treatment. However, with time and experience, most people learn how to make many of these 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 (www.uptodate.com/patients). 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: Type 1 diabetes in children (The Basics)
Patient education: Managing 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)
Patient education: Foot care for people with diabetes (The Basics)
Patient education: How to give an insulin shot (The Basics)
Patient education: How to use an insulin pen (The Basics)
Patient education: Checking your blood sugar at home (The Basics)
Patient education: Keeping track of your blood sugar (The Basics)
Patient education: How to dispose of needles and other sharps (The Basics)
Patient education: Blood glucose tests (The Basics)
Patient education: Diabetes and heart disease (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 chronic 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

(www.nlm.nih.gov/medlineplus/healthtopics.html)

●National Institute of Diabetes and Digestive and Kidney Diseases

(www.niddk.nih.gov/)

●American Diabetes Association (ADA)

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

(www.diabetes.org)

●Hormone Health Network

(www.hormone.org, available in English and Spanish)

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