Also called: Blood Glucose Meter
A glucose meter is a small, portable device designed for home use that checks glucose (blood sugar). The meter warns when blood glucose is out of range so people with diabetes can take immediate steps to correct it.
Keeping glucose close to the physician-prescribed target range can reduce or prevent the risk of diabetes complications such as damage to the eyes, kidneys, nerves and blood vessels. The meter also allows patients to monitor the effects of diet, exercise, stress and medications on glucose levels.
The meter reads a blood sample taken from a fingertip, arm, hand, abdomen, thigh or calf. It digitally displays the glucose level as a number in milligrams per deciliter (mg/dL) that can be recorded for glucose monitoring. Patients and their physicians can review the results and decide if the diabetes care plan is working. Some diabetic patients, particularly those who use insulin, need to test more than others. A glucose testing schedule should be designed for each individual patient by a physician.
Dozens of meters are available on the market. Models vary in size, speed, cost and ease of use, and they each have their own set of features. In choosing a meter, patients should consider the advantages and disadvantages of different models and ask their physician for advice on what meter is right for them. There have been many recent innovations, including a combination insulin pump and glucose meter that monitors glucose continually.
Accurate readings are essential for management of glucose. Mechanical and human error can cause inaccuracy. Glucose meters have various controls patients use to standardize the readings, including glucose control solutions and electronic meter controls.
Patients are advised to bring their glucose meter with them on diabetes appointments. When a meter reading is recorded a few minutes before blood is drawn for laboratory tests the results can be compared for accuracy. The physician can also view the patient’s testing method to ensure that self-tests are being completed properly.
Other glucose testing methods exist, including the glycohemoglobin test, but the glucose meter is the most accurate home method for assessing day-to-day glucose control. Researchers are developing noninvasive monitoring techniques.
About glucose meters
A glucose meter, also called a glucose monitor, is a small, portable device designed for home use that checks levels of glucose (blood sugar) for the management of diabetes. The meter warns people with diabetes when glucose levels are out of range.
Target blood glucose range is a personalized number given by a physician. It is usually based on factors such as age, presence of diabetic complications or other medical conditions, and tendency to have hypoglycemia unawareness (difficulty sensing symptoms of low glucose).
In general, normal plasma blood glucose levels for people with diabetes are 90 to 130 milligrams per deciliter (mg/dL) before meals and 110 to 150 mg/dL at bedtime. Whole blood readings are set at 80 to 120 mg/dL before meals and 110 to 150 mg/dL at bedtime, according to the American Diabetes Association (ADA).
Checking glucose levels with a typical meter requires a person to place a small sample of blood on a test strip. Test strips are coated in chemicals that combine with glucose. The strip is read by the monitor, which measures how much glucose is present. Meters measure glucose in different ways. Some measure the amount of electricity that can pass through the blood sample. Others measure how much light reflects from it. The meter digitally displays the glucose level as a number in milligrams per deciliter (mg/dL) that can be recorded for glucose monitoring.
The meter is matched to each new box of glucose testing strips through a process called coding. Manually coded meters require the user to enter a code number or insert a code strip or code chip into the device. Automatically coded meters set the correct code whenever a test strip is inserted and may result in greater accuracy.
Accurate readings are essential for management of glucose. Mechanical and human error can cause inaccuracy. Some meters come with a standard control solution that has a known concentration of glucose. The solution can be tested and compared to the meter’s results. Other monitors test accuracy with electronic controls. With this method a cartridge or special test strip is placed in the meter and a signal appears to indicate that the meter is working properly.
Patients are advised to bring their glucose meter with them on diabetes appointments. When a meter reading is recorded a few minutes before blood is drawn for laboratory tests, the results can be compared for accuracy.
To use most glucose meters, complete the following steps:
- Wash hands with soap and dry thoroughly. If drawing blood from an area besides the finger, wash and dry that area. If soap and water are not available, sterilize the sample site with alcohol.
- Prepare the meter. Because each meter works differently, read the instructions carefully.
- Choose the spot. Draw blood from different spots to allow healing.
- Prepare the lancet and lancing device. Finger-pricking devices vary, so read instructions carefully.
- Place the lancing device against the side of the finger or at an alternate site (area other than the finger) and press the button. Meters are different, so make sure the meter is approved for alternate site testing.
- Hold the hand down and hold the finger to squeeze out a drop of blood.
- Place the blood on the test strip and put the test strip in the meter according to the manufacturer’s directions. With some models the blood is placed on the strip after it has already been inserted into the meter. Read meter directions carefully.
- Use a gauze, tissue or cotton ball to wipe clean any blood and control bleeding at the puncture site.
- Record the results. Recorded meter results will tell a physician how a patient’s diabetes care plan is working. It will also allow the patient to monitor how food, exercise, stress and medicines affect glucose.
- Dispose of the lancet in a secure container with a lid.
Because not all glucose monitors work in the same way, patients should get training from a certified diabetes educator on how to use their meter and interpret results. The educator should supervise the test to ensure that the patient is using the meter properly. A physician can also periodically view the patient’s testing method to ensure that self-tests are being completed properly.
Choosing a glucose meter
There are dozens of models of glucose meters on the market. They differ in several ways including size of the blood sample needed for each test, speed, size, cost and ability to store test results over time.
To choose the right meter, patients should consider:
- Sample site (the places from which blood can be drawn for testing). Many meters meters use alternative site testing. Samples from the upper arm, forearm, hand, calf, abdomen and thigh require smaller blood samples and are less painful because these sites have fewer nerve endings than fingertips. However, blood in the fingertip is quicker to show changes in glucose (blood sugar) levels than blood in other parts of the body. Patients should be consistent in the sample site used to test glucose. Alternate sites should not be used if the glucose level is low, the patient is unaware of hypoglycemia or the test results differ from how the patient is feeling.
- Sample size (the amount of blood needed for testing). Meters that require a smaller blood sample may be easier for patients with poor circulation or those testing in a cold environment.
- Size of the meter. Meters come in smaller sizes for easier portability. However, smaller meters are easier to misplace and require more dexterity to use.
- Test timing (the amount of time until results are available). If test speed is an issue, some meters take as little as five seconds to report results, and others can take up to a minute.
- The patient’s dexterity. For those who have trouble with hand movements due to conditions such as diabetic neuropathy, some monitors require less handling, use larger testing strips or use strips that come in a vial rather than individually wrapped in foil.
- The patient’s vision. There are several monitors on the market for the visually impaired. Many people with diabetes have visual problems due to diabetic retinopathy, glaucoma or cataracts. There are meters available with large digital displays, and others guide the patient with spoken instructions.
- Support system. Some models come with an instructional video, and most companies offer a 24-hour toll-free number for customers who are having problems with their meter. Product support Web sites may also be available.
- Maintenance. Some monitors require more cleaning and upkeep than others.
- Meter memory (the amount of data that can be stored in the meter). For patients who have trouble keeping a written record of test results, many meters store results in memory. Some offer built-in data management systems that store hundreds of test results and other information including time, date, and the type and dose of insulin. However, the memory of a glucose meter cannot replace the glucose patterns over time information that is provided by a written record.
- Use of insulin. A possible option for patients who take insulin is a combined insulin pump and glucose meter that monitors glucose continuously. The U.S. Food and Drug Administration approved this device in 2006.
- Computer compatibility. Some meters connect to computers where patients can download their results. Some wireless models, designed primarily for children or people at risk of glucose control problems, can be monitored by parents, other loved ones or caregivers through e-mail or through text messaging to a cell phone or pager. Results from computerized glucose monitors can be easily printed for physician review and be transformed into simple graphs and charts.
- Language. Some meters can display in multiple languages.
- Battery replacement. Most models come with standard electronic equipment batteries that are easily replaceable. Others have batteries that are difficult or expensive to replace.
- Insurance coverage. Certain meters, control solutions and test strips may be covered by insurance. This will reduce personal costs.
- Expense. Consider sale prices, rebate offers and what insurance will cover. Some meters calibrate with generic test strips that are less expensive. Test strips are often more expensive in the long term than the meter itself. Patients should consider all costs when determining the preferred glucose meter.
- Calibration. The amount of chemical on test strips can vary from batch to batch. In order to ensure accuracy, most meters must be calibrated, or standardized with every new batch of strips. Some models calibrate automatically. Disposable meters that come with pre-loaded test strips do not need to be calibrated.
- Need or desire for other test results. Some meters test for lipids, ketones, cholesterol, glycated hemoglobin (A1C) and plasma glucose as well as whole blood glucose.
- Ease of use. Some meters require fewer steps to test than others.
- Blood contamination. People with diabetes and a blood-borne illness such as hepatitis or HIV can buy models with no-wipe strips that absorb the whole blood sample.
- Lighting. For people who often test in the middle of the night, some models come with spotlights, lighted displays and luminous covers.
Patients should consider the advantages and disadvantages of different models and ask a physician for advice on what meter is right for them. People may also want to consider obtaining two meters for convenience. Having one meter for home use and another one for work or school can eliminate the problem of carrying the meter around or forgetting it. Meters are often available at little or even no cost because the manufacturer makes a profit instead on the test strips. To achieve the most consistent results, the meters should be the same make and model and use the same test strips.
Potential risks of using a glucose meter
Though glucose meters play an essential role in self-monitoring of glucose (blood sugar), there is a higher risk of inaccurate readings with a meter than with blood glucose testing performed by a laboratory. Accurate results are essential for effective glucose management. Inaccurate readings can result in unnecessary changes to diabetes management plans and are usually caused by one of two factors:
- Meter malfunction. Meters and strips sometimes malfunction and give false results. Glucose meters should be tested a minimum of once a month. One way to test a machine and strips for accuracy is to use a standard control solution. These solutions have a known concentration of glucose that can be compared to a meter’s results.
Some meters test accuracy with electronic controls. With this method a cartridge or special test strip is placed in the meter and a signal appears to indicate that the meter is working properly.
Patients are advised to take their meter with them for diabetes appointments. When a meter reading is recorded a few minutes before blood is drawn for laboratory tests, the results can be compared for accuracy.
- Human error. Patients who do not properly use their glucose meters can also be responsible for inaccurate readings. To ensure that the user is testing properly, demonstrations should be done periodically in front of a physician or diabetes educator to refresh techniques even by highly experienced patients.
Other common causes of inaccurate readings include:
- Dirty or wet hands. Having dirt and food on fingers can affect meter readings.
- Sample size. A blood drop that is too small or any additional blood added to the strip after the initial drop can cause inaccurate readings.
- Calibration. The amount of reagent (chemical) on test strips can vary from batch to batch. To ensure accuracy, most glucose meters must be calibrated, or standardized, with every new batch of test strips. Failing to calibrate can lead to inaccuracy.
- Dirty meter. Check the meter’s manual for information on how and how often to clean the meter.
- Expired test strip. Test strips should not be considered accurate past their printed expiration date.
- Third-party test strips. Third-party or generic test strips are less expensive than the manufacturer’s test strips but may not work well for the meter. Contact the meter’s manufacturer for information on what test strips to use.
- Alcohol. When alcohol is used to sterilize the sample site, it must dry completely before blood is drawn or it can affect the reading.
- Abnormal amounts of hematocrit. Hematocrit is the amount of red blood cells in the blood. People with abnormal levels of hematocrit will test higher and lower for blood glucose than those with normal red blood cell amounts.
- Altitude, temperature and humidity. These environmental factors can have unpredictable effects on glucose results. High humidity can cause moisture to affect the strip. High and low temperatures can negatively affect the meter and the test strips. Test strips should not be removed from their packaging until the patient is ready to use them. The meter and test strips should be stored and handled according to manufacturer instructions.
- Interfering agents. Uric acid, vitamin C, glutathione (an antioxidant) and many medications (including aspirin, acetaminophen, estrogens, corticosteroids and antidepressants) in the blood can interfere with glucose testing. Each meter’s manual should list any substances that may interfere with testing accuracy.
- Age of the meter. Electrical components can begin to break down over time and affect precision. Check the meter’s manual for warranty information.
- Damage to the meter. Dropping a meter or other rough treatment can reduce its accuracy.
- Batteries. Low batteries in a meter can affect its performance.
- Technique. Inexperienced and experienced glucose meter users can make mistakes. Patients should review the manual for step-by-step instructions and perform periodic testing demonstrations in front of their diabetes educator.
- Whole blood vs. plasma. Blood glucose numbers vary on the type of blood being tested. Readings of plasma blood are usually 10 to 15 percent higher than readings of whole blood. Patients should be aware for which type of blood test they are reading results. The user’s manual should explain if the meter displays results as whole blood or plasma.
In rare cases an infection may develop at the puncture site. To minimize this risk, wash hands thoroughly. If blood is being drawn from a site other than the finger, wash that area as well. If soap and water are not available, clean the area with alcohol but allow drying before testing.
Alternatives to glucose meters
The glucose meter is not the only approach to testing glucose (blood sugar). However, it is considered the most accurate home method for measuring day-to-day glucose control.
Other home glucose testing methods 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 the blood glucose level.
- Visually readurine strips. Glucose can also be present in urine, and there are severalurine tests available on the market. Some require the strip to be dipped in 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.
- Glycohemoglobin test (A1C test). This test measures a person’s average blood glucose level over the past two to three months. Hemoglobin is a protein component of red blood cells that transports oxygen to the cells in the body. Hemoglobin combines with glucose to make glycosylated hemoglobin. The test shows the amount of glucose that sticks to the red blood cells, which is proportional to the amount of glucose in the blood. It can be said the test is reading the “memory” of the red blood cells’ activity. A diabetic patient’s typical target result for the A1C test is 7 percent or less, and testing is recommended at least twice a year.
- Visually read ketone urine strips. Ketones are in the urine if fat is being used instead of glucose for energy. This occurs because insulin is either not available or very low to break down glucose. Elevated ketones are one indication of uncontrolled diabetes. It is important to follow the directions and notify one’s physician of the results.
Future of glucose meters
Researchers are working on new ways to test glucose (blood sugar) without having to draw blood. One device recently approved by the U.S. Food and Drug Administration (FDA) is worn around the arm like a band. It provides continuous glucose monitoring by sampling perspiration from the skin with an electric current and measuring the glucose in the fluid. The results are displayed continuously, allowing the patient to closely monitor the glucose level up to 13 hours. An alarm will sound if blood glucose falls out of range.
This device has memory for this device can store up to 8,500 readings and requires a prescription. It is designed to enhance, not replace, conventional blood glucose monitoring. Patients would still have to self-test glucose levels.
The FDA has also approved continuous glucose monitoring (CGM) devices, most of which are inserted into abdominal skin, that check glucose levels every five minutes for up to three or seven days. These too are meant to supplement, not replace, fingerstick tests.
The FDA approved a combination insulin pump and continuous glucose monitor in 2006. It also has an alarm to warn of dangerous glucose levels. An ultimate goal for scientists is to develop a surgically implanted artificial pancreas that automatically adjusts doses of insulin according to the body’s needs, with no input from the patient.
Noninvasive blood glucose monitoring methods under development include:
- Shining light onto the skin or through body tissue. A laser lancing device has already been developed for use instead of a standard lancet.
- Measuring the infrared radiation given off by the body.
- Applying radio waves to the fingers.
- Using ultrasound.
- Checking the viscosity (thickness) of fluids in tissue underneath the skin.
Questions for your doctor about glucose meters
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 meters:
- How often should I test my blood glucose?
- At what times should I do this?
- What is my target glucose range?
- What should I do when my glucose is out of this range?
- Are there any particular features I should look for in a glucose meter?
- Am I a good candidate for a continuous glucose monitoring device?
- Am I a good candidate for a combined insulin pump and glucose meter?
- Do you recommend a certain model of glucose meter for me?
- Who will train me in using my meter?
- What kind of care does my glucose meter need? How often should it be calibrated?
- What sites should I take a blood sample from? How often should I rotate sites?
- What other glucose testing should I undergo, and how often?