Glucose Monitoring

Glucose Monitoring

Also called: Self Monitoring of Blood Glucose, Blood Glucose Monitoring, Blood Sampling Devices, Home Blood Glucose Monitoring

Summary

Glucose monitoring is the self-testing of glucose (blood sugar) levels for the management of diabetes. It usually involves placing a blood sample on a chemically coated test strip. The test strip is then placed in a glucose meter. The meter reads the sample and digitally displays the blood glucose level as a number.

Visually read blood and urine strips and home glycohemoglobin tests can also be used, but the glucose meter is considered the most accurate home method for measuring day-to-day glucose control.

People with diabetes should work to keep their glucose levels as close as possible to their physician-recommended target range. Maintaining healthy glucose levels can prevent hyperglycemia and hypoglycemia and can prevent or delay the onset of short-term and long-term diabetic complications.

Patients can manage their diabetes with methods that may include diet, exercise, insulin and anti-diabetic agents, as prescribed by their physician. Some patients, such as those who take insulin, must perform glucose monitoring several times a day, but for some others this is needed only occasionally. A physician can recommend a testing schedule including how often to test and at what times of the day.

Many factors can affect glucose levels including food, exercise, stress, medication and illness. Glucose monitoring is an effective way to spot changes in blood glucose levels and identify what is causing them. Patients should record their results in a log book and review them with their physician. The physician can then decide if changes are needed in the diabetes management plan.

There have been many recent innovations in checking glucose, including continuous glucose monitoring, which can now incorporate an insulin pump. Scientists are developing additional improvements using cellphones, implanted microchips and other technology.

About glucose monitoring

Glucose monitoring is a method of self-testing glucose (blood sugar) levels for the management of diabetes. It involves pricking the finger or an alternate site such as the arm or thigh for a sample of blood and placing that sample on a test strip. A glucose meter then analyzes the strip. The meter digitally displays the glucose level as a number in milligrams per deciliter (mg/dL).

Other methods of glucose monitoring exist, including visually read blood and urine strips and home glycohemoglobin tests. However, the glucose meter is considered the most accurate tool for measuring day-to-day glucose control at home.

People with diabetes should work to keep their glucose levels as close to normal as possible to feel their best and to avoid glucose irregularities such as hyperglycemia, hypoglycemia, insulin shock and unstable diabetes. Controlling glucose can prevent or delay the development of immediate complications such as unconsciousness and long-term complications such as diseases of the eyes, kidneys, nerves and blood vessels. People with diabetes can control their glucose with methods that may include diet, exercise, insulin and anti-diabetic agents, as prescribed by their physician.

Self-monitoring of blood glucose allows patients to record test results and, according to their physician-prescribed treatment plan, make healthy decisions about diet, exercise and medication dosage. Monitoring glucose provides important knowledge for the management of diabetes. Without monitoring, the patient is not informed of the balance between levels of insulin and glucose. People with diabetes and their physicians can examine patterns in glucose test results and judge if the diabetes management plan is working, or if changes need to be made.

All people with diabetes can benefit from glucose monitoring. It is especially important for diabetic patients who are:

  • Taking insulin or other diabetes medications
  • Pregnant
  • Having difficulty controlling glucose
  • Having ketones in urine from high blood glucose
  • Having low glucose without the normal warning signs (hypoglycemia unawareness)
  • Experiencing an illness

Steps to effective glucose monitoring include:

  • Know the target glucose range. For people with diabetes, the American Diabetes Association (ADA) recommends a glucose range of 80 to 120 mg/dL before meals and 100 to 140 mg/dL at bedtime for whole blood readings and 90 to 130 mg/dL before meals and 110 to 150 mg/dL at bedtime for plasma blood readings.

    However, this range is not appropriate for everyone. The target glucose range is a personalized number given by a physician. It is usually based on factors such as age, level of physical activity, presence of diabetic complications or other medical conditions such as heart failure, and whether there is a tendency to have hypoglycemia unawareness. Patients should aim to keep their glucose levels within their personalized range.
  • Learn how to check glucose. Ask a physician or certified diabetes educator for a demonstration.
  • Decide on a testing schedule. Some people with diabetes need to check their glucose more often than others, depending on the type of diabetes, medications and glucose levels. Ask a physician for advice on how often and at what times to test.
  • Keep a record of results. Patients should record test results in a log book along with medication dose. Changes in food, activity, illness, stress and medication should also be noted. Some physicians may instruct patients to fax in results. Some glucose meters store test results in memory or connect to computers where results can be downloaded. Once on the computer, results can be printed for physician review or turned into simple graphs and charts.
  • Look for glucose patterns. Review blood glucose records for trends in hyperglycemia or hypoglycemia. Take note if levels are too high or too low several days in a row at about the same time. Patterns can reveal conditions such as dawn phenomenon or the Somogyi effect. Glucose readings that are persistently above or below target range may mean that the diabetes management plan is not working and needs to be revised.
  • Investigate what causes changes in blood glucose levels. Review the log book for fluctuations and try to connect them with their triggers. Blood glucose levels can be affected by:
FactorPossible effect on
blood glucose levels
FoodIncrease
Insulin or antidiabetic agentDecrease
GlucagonIncrease
Non-diabetes medicationsIncrease, decrease or no effect
ExerciseDecrease (generally)
IllnessIncrease (generally)
StressIncrease
AlcoholDecrease
  • Decide how to get glucose levels back to target range. Patients should review their log book records with their physician and decide what changes are necessary in diet, exercise or medication.

Recent research suggests that half or more of diabetes patients have poor glycemic control and that many admit not checking their glucose often enough. Regular glucose monitoring is essential in avoiding serious consequences such as diabetic retinopathy and diabetic coma.

Scientists are trying to make glucose monitoring more convenient, comfortable and accurate. Available advances include:

  • Continuous glucose monitoring (CGM). The U.S. Food and Drug Administration (FDA) has approved several of these systems for adults, and researchers are developing others. A typical CGM device measures glucose every five minutes for up to three days and is intended for occasional use, not to replace fingerstick testing. A device approved by the FDA in 2007 allows monitoring for up to seven days. One CGM device is worn like a wristwatch; others are pager-size devices with a needle-like sensor that is inserted into abdominal skin. The information is stored in the monitor’s memory and then transferred to the physician’s computer.
  • Built-in glucose meters featured in some models of insulin pumps.
  • Combined CGM and insulin pump. In 2006 the FDA approved an insulin pump that incorporates continuous glucose monitoring. The ultimate goal is creation of a surgically implanted artificial pancreas that requires no input from the patient.

Emerging glucose-monitoring techniques include an implantable microchip using radiofrequency identification technology to measure and send data, and software that sends glucose and blood pressure readings by cellphone to a physician’s computer.

Methods of glucose monitoring

The glucose meter is the most popular method of glucose monitoring. Although other methods exist, the glucose meter is considered the most accurate home method for measuring day-to-day control of glucose (blood sugar).

A glucose meter, also called a glucose monitor, is a small, is a small, portable device that lets patients check their levels of blood glucose. Testing glucose with a typical meter requires a person to use a lancet and place a small sample of blood on a test strip. Test strips are coated in chemicals that combine with glucose. The meter then analyzes the strip.

Alternatives to the glucose meter include:

  • Visually read blood glucose strips. These strips require a blood sample to be applied to a chemically coated test strip. The test pad on the strip then changes color accordingly. The more glucose is present in the blood the greater the color change on the test pad. The user then compares the color on the test pad to a color chart on the side of the vial and estimates their level of blood glucose.

    Visually read blood strips are beneficial when patients forget their meter or when their meter is malfunctioning. They are also easier to use when traveling. However, healthcare experts recommend the use of glucose meters over visually read blood test strips because:
    • Comparing color patches is not as straightforward as reading a number on a glucose meter.
    • Visually read blood strips are less accurate than meters because they provide only a range and not an exact number. Although some experienced people can read the strips as accurately as a meter, most people are simply guessing.
    • Patients must be able to see subtle changes in color to use this test, which may not be possible for someone who is colorblind or has eye diseases such as diabetic retinopathy, glaucoma or cataracts. A meter does not use colors.
  • Comparing the test pad to the chart before it has finished changing color can result in inaccurate readings. Early readings are not possible with meters.
  • Visually read urine strips. Glucose can also be present in urine, and there are several urine tests available on the market. Some require the strip to be dipped into a cup of urine, and others need to be passed through a stream of urine. The chemically coated test pad then reacts with the glucose in the sample and changes color accordingly. The test pad is then compared to a color chart on the side of the vial.

    Like visually read blood strips, visually read urine strips are beneficial when patients forget their meter or when their meter is malfunctioning. They are also easier to use when traveling. Although urine testing is less intrusive than blood testing, it is less accurate. Urine strips should be used for glucose measuring only when blood testing is not an option. Among the drawbacks of visually read urine strips:
    • Hypoglycemia is not detected. The strips measure if blood glucose is too high but do not detect if it is too low because at lower levels glucose does not enter the urine.
    • Results are not current. Urine strips do not report what glucose levels are at the moment, but rather what they were several hours ago. Current readings are necessary for deciding insulin dosage, handling emergencies and evaluating treatment programs.
    • Results do not provide details. Urine strips do not report when levels were high or how high they were.
    • Results are not exact. Urine glucose levels are more of an average value than blood glucose levels.
    • Many factors can alter results. Aspirin, fluid intake, vitamin C, dehydration, and failure to fully empty the bladder on the previous trip to the bathroom may alter urine strip results.
    • Results are easier to misread. Like visual read blood strips, colorblindness or other visual difficulties can interfere with accurate reading, as can reading the strip before it has finished changing color. Comparing color patches is not as straightforward as reading a number from a glucose meter.
  • Glycohemoglobin test (A1C test). This test measures a person’s average blood glucose level over a two- to three-month period. Hemoglobin is a protein component of red blood cells that transports oxygen to the cells in the body. Hemoglobin combines with blood glucose to make glycosylated hemoglobin. The test shows the amount of glucose that sticks (glycates) to the red blood cells, which is proportional to the amount of glucose in the blood.

    Having a glycohemoglobin test several times a year is a good way to determine if glucose levels are under control. Patients who are not meeting their treatment goals should have the A1C test four times a year, or as recommended by their physician. Traditionally assessed in a physician’s office, glycohemoglobin can now be measured with home testing kits. Most require patients to take their own blood sample and mail it to a lab for results. At least one version allows patients to see an immediate digital reading, but it is a one-time-use test. However, home monitoring cannot replace the regular A1C test performed by a physician.

    Although glycohemoglobin testing can provide an idea of how well a patient’s diabetes management plan is working, it does not replace daily self-testing of blood glucose levels. Major drawbacks of solely using glycohemoglobin tests include:
    • Day-to-day glucose control is not measured
    • Insulin amounts cannot be adjusted based on A1C test results
    • Vitamins C and E, high levels of lipids and diseases of the liver and kidneys may cause inaccurate results
    • Anemia and other diseases that affect hemoglobin may cause inaccurate results

Frequency of glucose monitoring

People with diabetes need to consult their physician about often to test glucose (blood sugar) levels. Some patients must test more often than others. Testing three to four times a day, sometimes more, is usually recommended for people who take insulin, because their glucose levels tend to fluctuate more throughout the day. Patients may need to test more often if they are sick or have a change in their normal routine such as an increase in stress or exercise.

Patients aiming for normal or near-normal glucose levels may be advised by their physician to monitor four or more times a day. Studies have shown that when monitoring drops to less than four times a day, glucose control worsens.

People taking anti-diabetic agents will be advised to monitor frequently when their physician is trying to find the right dose or when there is a change in their diabetes care plan, such as an increase in insulin. Once a physician has decided if any changes are needed, recommended monitoring may be reduced to once or twice a day. When diabetes is managed without medications and glucose levels are under control, monitoring might be less frequent.

Useful times for glucose monitoring include:

  • Before meals or a big snack (preprandial). Insulin doses can be adjusted based on results.
  • One to two hours after meals or a big snack (postprandial). Results can show the effects of various foods on glucose levels. When a dose of rapid-acting insulin is taken before meal, results can show its effectiveness.
  • Before bedtime. When the reading is low, steps can be taken immediately to raise the level of blood glucose. Insulin doses can be adjusted if results continue to be low.
  • Early morning (2 or 3 a.m.). Early-morning blood glucose tests can provide information on overnight glucose. Insulin doses can be adjusted to prevent nighttime hypoglycemia. Immediate action can be taken to raise glucose levels.

Certain circumstances may result in unusual changes in glucose levels. During such time, additional glucose checks may be recommended. These include:

  • Sick days. During illness the body releases hormones to help fight the illness and to promote healing. These hormones can cause an increase in blood glucose.
  • Experiencing shakiness, sweating or other symptoms of low glucose. Results can confirm symptoms are due to hypoglycemia and not something else. Immediate steps can be taken to raise the level of glucose.
  • Experiencing increased thirst, increased urination or other symptoms of high glucose. Results can confirm symptoms are due to hyperglycemia and not something else. Immediate steps can be taken to lower glucose.
  • Menstruation. The hormone fluctuations during the cycle may influence fluctuations in blood glucose.
  • Before driving or operating heavy machinery (especially for patients taking insulin, sulfonylureas or meglitinides). Immediate action can be taken to raise glucose levels that are too low.
  • Increased stress. Stress can cause glucose levels to increase.
  • Increased physical activity. Exercise typically decreases the level of glucose but in some circumstances may increase it.
  • Taking new antidiabetic agents. Many medications may affect patients’ glucose levels or their ability to recognize warning signs of low glucose. Patients are encouraged to discuss these possibilities with their physician or pharmacist.
  • Experiencing frequent insulin reactions (bouts of hypoglycemia) overnight or waking up with very high glucose levels.
  • Change in diabetes management program, such as insulin schedule, eating plan or exercise plan.
  • Weight loss or gain.
  • Hypoglycemia unawareness. 
  • Pregnancy. A diabetic woman may also be advised by her physician to increase glucose monitoring if she is pregnant or thinking about becoming pregnant.
  • Glucose levels have been erratic, severely high or low.
  • Intensive insulin therapy.
  • Administration of glucagon. This emergency treatment for insulin shock (severe hypoglycemia) requires glucose monitoring to determine if an additional injection is needed and if the glucose level has stabilized.

Benefits and risks of glucose monitoring

All people with diabetes benefit from glucose monitoring. For example, people with type 1, type 2, gestational diabetes or other forms of diabetes who take insulin or anti-diabetic agents can judge how well these drugs are working. Monitoring provides information on how much medication is needed to counter the rise of glucose (blood sugar) after a meal. These medications may put a person at risk for low glucose (hypoglycemia). Monitoring will reveal if levels are too low.

Patients who manage diabetes with a diet and exercise plan can benefit from feedback on how well their exercise and food choices are working. During pregnancy, glucose monitoring guides the treatment adjustments necessary to keep the woman and her fetus healthy.

Glucose monitoring is an effective way to control levels of blood glucose and offers many possible benefits to diabetes patients. Potential benefits of glucose monitoring include:

  • Detecting and preventing hyperglycemia (high glucose), hypoglycemia and insulin shock.
  • Preventing or delaying long-term complications of diabetes, including diseases of the eyes, kidneys, nerves and blood vessels.
  • Uncovering the effects of food, exercise, stress, illness, insulin and other medications and other factors on glucose levels.
  • Keeping track of glucose levels over time and determining trends and patterns.
  • Assisting in making day-to-day decisions for glucose management, including meal size and dosage of insulin and other medication.
  • Confirming that suspicions of low or high glucose are accurate and not the result of something unrelated to diabetes.
  • Alerting to emergency situations so immediate action can be taken to lower or raise levels of glucose.
  • Determining the need for starting insulin therapy. 
  • Identifying where changes in the diabetes management plan are needed.
  • Deciding what action is needed when a person is suffering from an illness.

The potential risks associated with glucose monitoring involve use of a glucose meter. A number of factors can make meter readings inaccurate, including machine malfunctions or human error.

Questions for your doctor

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about glucose monitoring:

  1. How often should I check my glucose?
  2. At what times of the day should I monitor my glucose?
  3. What is my target glucose range?
  4. What should I do when my glucose is too high or low?
  5. What factors can affect my glucose levels?
  6. Under what circumstances do I need to check my glucose more closely than usual?
  7. Which type of glucose monitor do you recommend for me?
  8. Do suggest any particular features or brand?
  9. Are there any recent or soon-to-come innovations in glucose monitoring that could benefit me?
  10. When is it OK for me to use a visually read blood test or a urine test to monitor glucose?
  11. Should I monitor my glycohemoglobin with a home testing kit?
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