Patient information: Self-blood glucose monitoring

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Patient information: Self-blood glucose monitoring
November 27, 2006
David K McCulloch, MD
UpToDate website

INTRODUCTION Û People with diabetes have an important role in their own medical care, and self-glucose monitoring is an opportunity for people with diabetes to take control of their 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 glucose levels in the normal or near-normal range. Monitoring blood glucose levels is one of the best ways of determining how well a diabetes treatment plan is working.

A healthcare provider will periodically order laboratory blood tests to determine blood glucose levels and hemoglobin A1c (A1C). The results of these tests give an overall sense of how blood glucose levels are controlled (show figure 1). However, fine-tuning of blood glucose levels and treatment also requires that patients monitor their own blood glucose levels on a day-to-day basis.

Self-blood glucose monitoring allows a person to know their blood glucose level at any time and helps prevent the immediate and potentially serious consequences of very high or very low blood glucose. Monitoring also enables tighter blood glucose control, which decreases the long-term risks of diabetic complications.

HOW TO TEST Û The following steps include general guidelines for testing blood glucose levels; specific details for individual blood glucose monitors should be obtained from the package insert or a healthcare provider.

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 the fingertip or alternate site (like the skin of the forearm) (show 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 (show picture 2).
Patients who have difficulty getting a good drop of blood from the fingertip can try rinsing the 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 TESTING Û Studies have proven that people with type 1 and 2 diabetes who maintain normal or near normal blood glucose levels have a lower risk of diabetes-related complications. The frequency of monitoring will depend upon the type of diabetes (1 or 2) and treatment used (insulin versus oral medications).

Type 1 diabetes Û For people with type 1 diabetes, frequent testing is the only way to safely and effectively manage blood glucose levels. (See "Patient information: Diabetes mellitus, type 1").

The recommended frequency of testing varies from one person to another, although most people need to test at least four times per day. People who use intensive insulin therapy and women with type 1 diabetes who are pregnant may need to test as many as seven times per day. (See "Patient information: Care during pregnancy for women with type 1 or 2 diabetes")

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 glucose control. However, people who like to track data using meters with a memory function may have difficulty if blood glucose results are on different meters.

Type 2 diabetes Û Blood glucose monitoring is also important for people with type 2 diabetes. The recommendations for frequency of testing vary from one person to another 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 to determine how frequently to test. (See "Patient information: Diabetes mellitus, type 2").

INTERPRETING RESULTS

Blood glucose testing Û The results of blood glucose testing indicate if diabetes treatments are on target. However, blood glucose results can be affected by activity levels, foods eaten, and medications (include insulin and oral diabetes medications). To interpret results, it is important to consider all of these factors.

Blood glucose results should be reviewed regularly with a healthcare provider. This discussion should include how to record results (either with paper and pen or electronically) and how to use results to optimally control blood glucose levels. Many meters have a memory function that allows results to be stored and downloaded to a computer. Results can then be analyzed and printed for a healthcare provider to review. These blood glucose records should be reviewed at each healthcare provider visit.

The record should include the time and date, blood glucose results, and dose of medication used; additional notes about food intake, exercise, and difficulties with illness or stress can also be helpful but are not generally required every day.

Several days of monitoring are usually needed to identify daily patterns, which can be used to make lifestyle or medication adjustments. People who use intensive insulin therapy should adjust their insulin dose before meals based upon the blood glucose readings (ie, give a higher dose of very-rapid or rapid acting insulin when blood glucose levels are high).

Need for urine testing Û People with type 1 diabetes should perform urine testing for ketones if the blood glucose level is above 240 mg/dL (13.3 mmol/L), during periods of illness or stress, or if there are 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 break down glucose, 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, which can lead to serious complications such as diabetic coma.

Urine ketone testing is done with a dipstick, available in pharmacies without a prescription. Urine can be collected and then tested with the dipstick, or the dipstick may be held in the urine stream. A color change occurs if ketones are present, indicating a trace, small, moderate, or large concentration of ketones. If a moderate to large concentration of ketones is present, the patient should consult with a healthcare provider immediately to determine the best treatment. An additional dose of insulin may be required, or the provider may instruct the patient to go to the nearest emergency room.

ADJUSTING TREATMENT Û Home blood glucose monitoring can provide useful and motivating information. However, the information should be used to make slow and careful changes to treatment, allowing the body time to respond to changes. Most people will need to consult with their provider frequently as they learn to make adjustments in treatment, especially with insulin. However, with time and experience, most people are able to learn how to make adjustments on their own.

Avoid making multiple treatment changes at the same time unless instructed to do so by a healthcare provider. Changing one aspect of treatment at a time allows for more careful evaluation of the effects of that change on blood glucose levels. Furthermore, it can take several days before changes are reflected in blood glucose results.

ACCURACY OF HOME GLUCOSE MONITORING Û Accuracy refers to the ability of a system to report a result that reflects the actual blood glucose level. Accuracy 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 the home monitor to check the blood glucose at the same time that a laboratory blood glucose level is drawn.

Hospital or office laboratories report glucose levels in part of the blood, called plasma. Most blood glucose monitors also report plasma results (this should be stated on the test strip or glucose monitor packaging). Older meters reported whole blood glucose results, which can differ from plasma results by as much as 15 percent. 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 the monitor, blood glucose strips, or monitoring technique.

Blood glucose meters Û 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 seems incompatible with physical symptoms (or lack of 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 hypoglycemia (low blood sugar).

Blood glucose strips Û Some brands of glucose strips have batch-to-batch variations. These variations may require that the meter is recalibrated every time a new batch of strips is opened. Never mix different batches of strips together, and quickly recap the container after removing a strip. Individually wrapped strips tend to be more reliable, but are also more expensive.

Alternate site testing Û Blood glucose results can be less accurate if sites other than the fingertips are used for testing (eg, arm, hand, leg). This should not be a problem if the person uses one site exclusively. However, when the blood glucose is rising rapidly (eg, immediately after eating) or falling rapidly (in response to rapidly acting insulin or exercise), blood glucose results from alternate sites may give significantly different results than a fingerstick reading. In these situations, fingertip testing is preferred.

Help for people with vision impairment Û People with vision impairment sometimes have difficulty using glucose meters. Patients with impaired vision can get assistance from the American Association of Diabetes Educators (AADE) at (800) 338-3633.

SELECTING A BLOOD GLUCOSE MONITOR Û There is no single blood glucose monitor that is better than others. A number of factors should be considered when choosing a monitor:

Expense Û 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 Û 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 Û Glucose meters take a reading from a drop of blood applied to strip. Older meters require more careful preparation of the strip and leave more room for error. Newer meters perform more of the steps automatically, so there is less room for error. Newer meters typically provide the most reliable monitoring results.
Sophistication Û Some meters allow entry of events (like eating or exercising) and come with software programs that allow the data to be downloaded to a computer. This is most helpful for people who test frequently and use intensive insulin treatment.
CONTINUOUS GLUCOSE TESTING Û Researchers are currently evaluating continuous, less invasive, and less intrusive methods of glucose testing.

How it works Û Continuous glucose monitoring systems (CGMS) use a glucose sensor (contained in a small needle) to determine the level of glucose in the interstitial fluid, found between cells under the skin. The sensor wirelessly transmits results to a small recording device (the size of a pager or cell phone), which can be worn on the clothing, carried in a purse, or placed within a short distance of the sensor (eg, a bedside table). The sensor records and displays the blood glucose level every few minutes, allowing the patient to observe the trend of their blood glucose levels. The receiver can also be set to alarm if the blood glucose 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 (hypoglycemia).

The sensor must be removed and reinserted in a different area approximately once per week. The person must continue to measure blood glucose levels with a traditional monitor 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.

Drawbacks Û 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 [5] . The CGMS tends to be less accurate in the lower glucose range (<70 mg/dL or 3.9 mmol/L) and may be inadequate for reliably detecting hypoglycemia.

Thus, continuous glucose sensing devices should not be relied upon exclusively to give information about 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.

WHERE TO GET MORE INFORMATION Û Your healthcare provider is the best source of information for questions and concerns related to your medical problem. Because no two patients are exactly alike and recommendations can vary from one person to another, it is important to seek guidance from a provider who is familiar with your individual situation.