Diabetes: Choosing and Using Your Glucose Meter
- Choosing a glucose meter
- Using your glucose meter
- Important features of glucose meters
- Factors that affect glucose meter performance
- Making sure your meter works properly
- User experiences with glucose meters
- New technologies, alternative site testing
- Minimally invasive and non-invasive glucose meters
- How FDA regulates glucose meters
- Other diabetes management tests
The process of monitoring one's own blood glucose with a glucose meter is often referred to as self-monitoring of blood glucose or "SMBG." To test for glucose with a typical glucose meter, place a small sample of blood on a disposable "test strip" and place the strip in the meter. The test strips are coated with chemicals (glucose oxidase, dehydrogenase, or hexokinase) that combine with glucose in blood. The meter measures how much glucose is present. Meters do this in different ways. Some measure the amount of electricity that can pass through the sample. Others measure how much light reflects from it. The meter displays the glucose level as a number. Several new models can record and store a number of test results. Some models can connect to personal computers to store test results or print them out.
Choosing a Glucose Meter
At least 25 different meters are commercially available. They differ in several ways including:
- Amount of blood needed for each test
- Testing speed
- Overall size
- Ability to store test results in memory
- Cost of the meter
- Cost of the test strips used
Newer meters often have features that make them easier to use than older models. Some meters allow you to get blood from places other than your fingertip (alternative site testing). Some new models have automatic timing, error codes and signals, or barcode readers to help with calibration. Some meters have a large display screen or spoken instructions for people with visual impairments.
Using Your Glucose Meter
Diabetes care should be designed for each individual patient. Some patients may need to test (monitor) more often than others do. How often you use your glucose meter should be based on the recommendation of your health care provider. Self-monitoring of blood glucose (SMBG) is recommended for all people with diabetes, but especially for those who take insulin. The role of SMBG has not been defined for people with stable type 2 diabetes treated only with diet.
As a general rule, the American Diabetes Association (ADA) recommends that most patients with type 1 diabetes test glucose three or more times per day. Pregnant women taking insulin for gestational diabetes should test two times per day. ADA does not specify how often people with type 2 diabetes should test their glucose, but testing often helps control.
Often, self-monitoring plans direct you to test your blood sugar before meals, 2 hours after meals, at bedtime, at 3 a.m., and anytime you experience signs or symptoms. You should test more often when you change medications, when you have unusual stress or illness, or in other unusual circumstances.
Learning to Use Your Glucose Meter
Not all glucose meters work the same way. Since you need to know how to use your glucose meter and interpret its results, you should get training from a diabetes educator. The educator should watch you test your glucose to make sure you can use your meter correctly. This training is better if it is part of an overall diabetes education program.
Instructions for Using Glucose Meters
The following are the general instructions for using a glucose meter:
- Wash hands with soap and warm water and dry completely or clean the area with alcohol and dry completely.
- Prick the fingertip with a lancet.
- Hold the hand down and hold the finger until a small drop of blood appears; catch the blood with the test strip.
- Follow the instructions for inserting the test strip and using the SMBG meter.
- Record the test result.
FDA requires that glucose meters and the strips used with them have instructions for use. You should read carefully the instructions for both the meter and its test strips. Meter instructions are found in the user manual. Keep this manual to help you solve any problems that may arise. Many meters use "error codes" when there is a problem with the meter, the test strip, or the blood sample on the strip. You will need the manual to interpret these error codes and fix the problem.
You can get information about your meter and test strips from several different sources. Your user manual should include a toll free number in case you have questions or problems. If you have a problem and can't get a response from this number, contact your healthcare provider or a local emergency room for advice. Also, the manufacturer of your meter should have a website. Check this website regularly to see if it lists any issues with the function of your meter.
New devices are for sale such as laser lancets and meters that can test blood taken from "alternative sites" of the body other than fingertips. Since new devices are used in new ways and often have new use restrictions, you must review the instructions carefully.
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Important Features Of Glucose Meters
There are several features of glucose meters that you need to understand so you can use your meter and understand its results. These features are often different for different meters. You should understand the features of your own meter.
Measurement Range. Most glucose meters are able to read glucose levels over a broad range of values from as low as 0 to as high as 600 mg/dL. Since the range is different among meters, interpret very high or low values carefully. Glucose readings are not linear over their entire range. If you get an extremely high or low reading from your meter, you should first confirm it with another reading. You should also consider checking your meter's calibration.
Whole Blood Glucose vs. Plasma Glucose. Glucose levels in plasma (one of the components of blood) are generally 10-15% higher than glucose measurements in whole blood (and even more after eating). This is important because home blood glucose meters measure the glucose in whole blood while most lab tests measure the glucose in plasma. There are many meters on the market now that give results as "plasma equivalent". This allows patients to easily compare their glucose measurements in a lab test and at home. Remember, this is just the way that the measurement is presented to you. All portable blood glucose meters measure the amount of glucose in whole blood. The meters that give "plasma equivalent" readings have a built in algorithm that translates the whole blood measurement to make it seem like the result that would be obtained on a plasma sample. It is important for you and your healthcare provider to know whether your meter gives its results as "whole blood equivalent" or "plasma equivalent."
Cleaning. Some meters need regular cleaning to be accurate. Clean your meter with soap and water, using only a dampened soft cloth to avoid damage to sensitive parts. Do not use alcohol (unless recommended in the instructions), cleansers with ammonia, glass cleaners, or abrasive cleaners. Some meters do not require regular cleaning but contain electronic alerts indicating when you should clean them. Other meters can be cleaned only by the manufacturer.
Display Of High And Low Glucose Values. Part of learning how to operate a meter is understanding what the meter results mean. Be sure you know how high and low glucose concentrations are displayed on your meter.
Factors That Affect Glucose Meter Performance
The accuracy of your test results depends partly on the quality of your meter and test strips and your training. Other factors can also make a difference in the accuracy of your results.
Hematocrit. Hematocrit is the amount of red blood cells in the blood. Patients with higher hematocrit values will usually test lower for blood glucose than patients with normal hematocrit. Patients with lower hematocrit values will test higher. If you know that you have abnormal hematocrit values you should discuss its possible effect on glucose testing (and HbA1C testing) with your health care provider. Anemia and Sickle Cell Anemia are two conditions that affect hematocrit values.
Other Substances. Many other substances may interfere with your testing process. These include uric acid (a natural substance in the body that can be more concentrated in some people with diabetes), glutathione (an "anti-oxidant" also called "GSH"), and ascorbic acid (vitamin C). You should check the package insert for each meter to find what substances might affect its testing accuracy, and discuss your concerns with your health care provider.
Altitude, Temperature and Humidity. Altitude, room temperature, and humidity can cause unpredictable effects on glucose results. Check the meter and test strip package insert for information on these issues. Store and handle the meter and test strips according to the instructions.
Third-Party Test Strips. Third-party or "generic glucose reagent strips" are test strips developed as a less expensive option than the strips that the manufacturer intended the meter to be used with. They are typically developed by copying the original strips. Although these strips may work on the meter listed on the package, they could look like strips used for other meters. Be sure the test strip you use is compatible with your glucose meter.
Sometimes manufacturers change their meters and their test strips. These changes are not always communicated to the third-party strip manufacturers. This can make third-party strips incompatible with your meter without your knowledge. Differences can involve the amount, type or concentration of the chemicals (called "reagents") on the test strip, or the actual size and shape of the strip itself. Meters are sensitive to these features of test strips and may not work well or consistently if they are not correct for a meter. If you are unsure whether or not a certain test strip will work with you meter, contact the manufacturer of your glucose meter.
Making Sure Your Meter Works Properly
You should perform quality-control checks to make sure that your home glucose testing is accurate and reliable. Several things can reduce the accuracy of your meter reading even if it appears to still work. For instance, the meter may have been dropped or its electrical components may have worn out. Humidity or heat may damage test strips. It is even possible that your testing technique may have changed slightly. Quality control checks should be done on a regular basis according to the meter manufacturer's instructions. There are two kinds of quality control checks:
Check Using "Test Quality Control Solutions" or "Electronic Controls".
- Test quality control solutions and electronic controls are both used to check the operation of your meter. Test quality control solutions check the accuracy of the meter and test strip. They may also give an indication of how well you use your system. Electronic controls only check that the meter is working properly.
- Test quality control solutions have known glucose values. Essentially, when you run a quality control test, you substitute the test solution for blood. The difference is that you know what the result should be.
- To test your meter with a quality control solution, follow the instructions that accompany the solution. These will guide you to place a certain amount of solution on your test strip and run it through your meter. The meter will give you a reading for the amount of glucose in the sample. Compare this number to the number listed on the test quality control solution. If the results of your test match the values given in the quality control solution labeling, you can be assured the entire system (meter and test strip) is working properly. If results are not correct, the system may not be accurate--contact the manufacturer for advice.
- Manufacturers sometimes include quality control solution with their meter. However, most often you must order it separately from a manufacturer or pharmacy.
- Some glucose meters also use electronic controls to make sure the meter is working properly. With this method, you place a cartridge or a special "control" test strip in the meter and a signal will appear to indicate if the meter is working.
Take Your Meter with You to The Health Care Provider's Office. This way you can test your glucose while your health care provider watches your technique to make sure you are using the meter correctly. Your healthcare provider will also take a sample of blood and evaluate it using a routine laboratory method. If values obtained on the glucose meter match the laboratory method, you and your healthcare provider will see that your meter is working well and that you are using good technique. If results do not match the laboratory method results, then results you get from your meter may be inaccurate and you should discuss the issue with your healthcare provider and contact the manufacturer if necessary.
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User Experiences with Glucose Meters
The FDA's Center for Devices and Radiological Health (CDRH) held a series of focus groups on blood glucose meter use in 2001. The twenty-two members participated in six groups. They were all government employees, mostly from CDRH. They were either people with diabetes or family members of people with diabetes who were familiar with the use of glucose meters.
Most of the participants in these groups were satisfied with their meters. Some were quite enthusiastic about the new models. A few had some concerns about meters. One such participant stated: "The first meter I got I couldn't use because it was too difficult."
Repeating Tests. Most users repeated tests now and then because they believed the first test result was incorrect. Users questioned test results based on their expectations about what the results should be. If the glucose level seemed "off," they repeated the test.
The ability to judge whether or not a test seemed accurate appeared to come from the users' experiences with their meters. These experiences helped them know how they felt when their glucose level was high, when it was low and when it was about right. They also were aware of what and when they had eaten, exercised, slept, or taken insulin, and they learned to anticipate the effect these activities have on their glucose levels.
Comments users made about their results include the following:
- I sometimes get a reading of perhaps 300 and then 180 on a retest. This happens in about 1 in 50 tests.
- Glucose tablet residue on my finger can throw results way off.
- I get some inaccurate readings - especially when the meter is new.
- Sometimes I get higher readings than I expect, probably because the meter was left out of the case or food got on it.
- The date wears off of the vial and I end up using expired strips.
- Humidity around the bathroom seems to affect performance of the strips.
- If I have wet hands, my results tend to be higher than expected.
Besides repeating tests because of a suspected inaccuracy in the first test, a frequent reason to repeat a test was that the meter indicated "insufficient blood" on the test strip and would not complete the test on the first attempt. When this happens, users needed to do another fingerstick. Users whose meters required less blood did not have this problem as often.
Feelings about Fingersticks. Surprisingly, most of the participants stated that fingerstick discomfort was not a big concern - even with children: "At first, fingersticks were a real problem, but now it doesn't bother her."
Most participants stated that discomfort was an issue when they first started to use the meter; this was especially true for children, but that the discomfort grew less important after a few weeks or months of use.
However, one participant of a "fragile" child with diabetes stated: "We test 8 to 10 times a day. He was losing sensitivity in his fingertips [from the frequent fingersticks]. We prefer the meter that allows testing in alternative sites."
Use of Test Solution. Most users did not use test solution often. Some never used it. They stated that the solution was difficult to use because it expired in a month, it was difficult to order, and they were not convinced that it helped.
Important Features. Users discussed and rated aspects of meters such as accuracy, ease-of-use, cost of the meter, cost of test strips, size, whether it was recommended by a friend etc. The most important consideration in this group was accuracy. This was followed by "ease of use" and then affordability.
Sampling blood from alternative sites may be desirable, but it may have some limitations. Blood in the fingertips show changes in glucose levels more quickly than blood in other parts of the body. This means that alternative site test results may be different from fingertip test results not because of the meter's ability to test accurately, but because the actual glucose concentration can be different. FDA believes that further research is needed to better understand these differences in test values and their possible impact on the health of people with diabetes.
Glucose concentrations change rapidly after a meal, insulin or exercise. Glucose levels at the alternative site appear to change more slowly than in the fingertips. Because of this concern, FDA has now requested that manufacturers either show their device is not affected by differences between alternative site and fingertip blood samples during times of rapidly changing glucose, or alert users about possible different values at these times.
Recommended labeling precautions include these statements:
- Alternative site results may be different than the fingertip when glucose levels are changing rapidly (e.g. after a meal, taking insulin or during or after exercise).
- Do not test at an alternative site, but use samples taken from the
- you think your blood sugar is low,
- you are not aware of symptoms when you become hypoglycemic, or
- the site results do not agree with the way you feel.
In October, 2001, FDA held a public meeting to discuss the types of information and labeling needed for glucose measuring devices if the blood sample is taken from alternative sites rather than the fingertip. Presenters included manufacturers of blood glucose meters, healthcare providers, people with diabetes, and parents of children with diabetes.
Minimally Invasive and Non-Invasive Glucose Meters
Researchers are exploring new technologies for glucose testing that avoid fingersticks. One of these is based on near-infrared spectroscopy for measurement of glucose. Essentially, this amounts to measuring glucose by shining a beam of light on the skin. It is painless. There are increasing numbers of reports in the scientific literature on the challenges, strengths, and weaknesses of this and other new approaches to testing glucose without fingersticks.
FDA has approved one "minimally invasive" meter and one "non-invasive" glucose meter. Neither of these should replace standard glucose testing. They are used to obtain additional glucose values between fingerstick tests. Both devices require daily calibration using standard fingerstick glucose measurements and both remain the subject of continuing studies to find how they are best used as tools for diabetes management.
- MiniMed Continuous Glucose Monitoring System. The MiniMed system consists of a small plastic catheter (very small tube) inserted just under the skin. The catheter collects small amounts of liquid that is passed through a "biosensor" to measure the amount of glucose present.
Minimed is intended for occasional use and to discover trends in glucose levels during the day. It does not give you readings for individual tests and therefore you can't use it for typical day-to-day monitoring. The device collects measurements over a 72-hour period and then must be downloaded by the patient or healthcare provider. Understanding trends over time might help patients know the best time to do their standard fingerstick tests. You need a prescription to buy MiniMed.
- Cygnus GlucoWatch Biographer. GlucoWatch is worn on the arm like a wristwatch. It pulls tiny amounts of fluid from the skin and measures the glucose in the fluid without puncturing the skin. The device requires 3 hours to warm up after it is put on. After this, it can provide up to 3 glucose measurements per hour for 12 hours. Unlike the MiniMed device, the GlucoWatch displays results that can be read by the wearer, although like the MiniMed device, these readings are not meant to be used as replacements for fingerstick-based tests. The results are meant to show trends and patterns in glucose levels rather than report any one result alone. It is useful for detecting and evaluating episodes of hyperglycemia and hypoglycemia. However, you must confirm its results with a standard glucose meter before you take corrective action. You need a prescription to buy GlucoWatch.
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How FDA Regulates Glucose Meters
FDA reviews all glucose meters and test strips before they can be marketed to the public. This FDA "premarket" review process requires the manufacturer of the meter to show that the meter system provides acceptable accuracy and consistency of glucose measurement at high, medium and low levels of glucose as compared to glucose meters already being sold. The quality of software is an increasingly important feature of glucose meters since it controls the testing and data storage and controls the displays that the user sees and uses when testing.
FDA also considers possible interference from over-the-counter medications, prescription medications, and vitamin supplements.
FDA also asks for data showing how well the meter has performed during actual use (a type of human factors study). These studies ensure that users understand the labeling, achieve good results, and avoid experiencing problems that could affect their health.
Reporting Problems with Glucose Meters to FDA
FDA learns about problems with medical products through the MedWatch program. Consumers can report problems with medical devices, including glucose meters, through MedWatch.
For general information about the MedWatch program and instructions for reporting problems with medical devices, use the following link:
MedWatch: The FDA Safety Information and Adverse Event Reporting Program http://www.fda.gov/medwatch/how.htm
For further information about how medical device problems are reported to FDA, use the following link:
Reporting Problems with Medical Devices http://www.fda.gov/cdrh/mdr.html
Performance Goals for Glucose Meters
Deciding performance standards for glucose meters has been controversial and challenging. In spite of effort in the late 1970s and 1980s by both FDA and CDC, no universally accepted standards or testing methods have been developed for the measurement of glucose. CDC (Centers for Disease Control and Prevention) recently held a standards conference and is exploring the possibility of developing a standard reference material for whole blood.
The ADA has recommended accuracy goals twice over the past twenty years, once in 1986 (target accuracy of +/- 15%) and once in 1993 (target accuracy of +/- 5%) No company that manufacturers glucose meters has developed a cost-effective system to meet these goals. A number of alternative standards have been suggested by national standards organizations in the U.S., Canada, and Europe. An international standard ISO DIS 15197 is currently under development that recommends accuracy of +/- 20 mg/dl for glucose values under 100 mg/dl and +/- 20% for higher glucose values.
Although data on glucose meters continue to show variable performance, the newest generations of meters are simpler to use and more accurate than older models. Improvements in the chemical, mechanical and software components of glucose meters are continuing to help with the management of diabetes.
Other Diabetes Management Tests
There is hemoglobin in all red blood cells. Hemoglobin is the part of the red blood cell that carries oxygen to the tissues and organs in the body. Hemoglobin combines with blood glucose to make glycosylated hemoglobin or hemoglobin A1c.
Red blood cells store glycosylated hemoglobin slowly over their 120-day life span. When you have high levels of glucose in your blood, your red blood cells store large amounts of glycosylated hemoglobin. When you have normal or near normal levels, your red blood cells store normal or near normal amounts of glycosylated hemoglobin. So, when you measure your glycosylated hemoglobin, you can find out your level of blood glucose, averaged over the last few months.
Doctors have used the glycosylated hemoglobin test for patients with diabetes since 1976 (1,2). The test is now widely used in the routine monitoring of patients with diabetes mellitus. Your doctor may use this test to see how well you respond to treatment. If you have low test values you probably have lowered risk for having complications from diabetes mellitus.
It is good to have your glycosylated hemoglobin tested at least two times a year if you meet your treatment goals or up to four times a year if you change therapy or do not meet your treatment goals. There are now many different ways to measure glycosylated hemoglobin. These tests vary in cost and convenience and you can do some at home. The values (glycosylated hemoglobin index) these tests give can vary too. Talk to your doctor about what your glycosylated hemoglobin index should be.
Patients with diseases affecting hemoglobin, such as anemia, may get wrong values with this test. Vitamins C and E, high levels of lipids, and diseases of the liver and kidneys may all cause the test results to be wrong.
Glycosylated Serum Proteins
Serum proteins, like hemoglobin, combine with glucose to form glycosylated products. Testing these glycosylated products can give information about your glucose control over shorter periods of time than testing glycosylated hemoglobin.
One common test is the fructosamine test. It gives information on your glucose status over a one- to two-week period. High values mean your blood glucose was high over the past two weeks. This test is good for watching short-term changes in your glucose status during pregnancy or after major changes in your therapy. There is no general guideline for when to use this test. Talk to your doctor about whether this test is right for you.
If you have any other disease that can change your serum proteins or if you have large amounts of Vitamin C (ascorbic acid) in your diet, these tests may give wrong values.
Only patients who are unable to use blood glucose meters should use urine glucose tests. Testing urine for glucose, which was once the best way for patients to manage their diabetes, has mostly now been replaced by self-monitoring of blood glucose. There are three major drawbacks of urine glucose testing compared to blood testing. First, urine glucose testing will not tell you about low (below 180 mg/dl) glucose levels, since at lower levels glucose does not enter your urine. Second, urine glucose readings change when the volume of your urine changes. Third, your urine glucose level is more of an average value than your blood glucose level. There are several dipstick tests available on the market.
Urine and Blood Ketones
When the body does not have enough insulin, fats are used for fuel instead of glucose. A by-product of burning fats is the production of ketones. Ketones are passed in the urine and can be detected with a urine test.
If you do not have diabetes, you usually have only small amounts of ketones in your blood and urine. If you have diabetes, however, you may have high amounts of ketones and acid, a condition known as ketoacidosis. This condition can cause nausea, vomiting, or abdominal pain and can be life threatening.
You may use urine dipsticks to rapidly and easily measure the ketones in your urine. You dip a dipstick in your urine and follow the instruction on the package to see if you have a high amount of ketones.
If you have type 1 diabetes, are pregnant with preexisting diabetes, or who have diabetes caused by pregnancy (gestational diabetes), you should check your urine for ketones. If you have diabetes and are ill, under stress, or have any symptoms of high ketones, you should also test your urine for ketones.
Results of ketone testing should be interpreted with care. High ketone levels are found when patients are pregnant (in the first morning urine sample), starving, or recovering from a hypoglycemic episode.
There are now tests for measuring ketones in blood that your doctor may use or you can use at home. Some measure a specific ketone (beta-hydroxybuyric acid) that patients with diabetic ketoacidosis may have.
It is still not known which type of ketone test -blood or urine-- offers more aid to people with diabetes.
One common and extremely serious result of diabetes is kidney failure. Under normal conditions, the kidneys filter toxins from the blood. When the kidney's filtering processes begin to become impaired, protein (microalbumin) begins to spill into the urine. Testing urine for small, yet abnormal amounts of albumin (microabluminuria) is a common way to detect this condition early, before it can damage your kidneys.
Many urine dipsticks are used to test for large amounts of albumin. To measure a small amount of albumin, which may show an early stage of kidney disease, your health care provider may use specific tests for low levels of albumin (microalbumin tests). To do this test, you may have to collect your urine for several 24-hour periods.
The ADA recommends that adults with diabetes be tested for microalbumin every 3- to 6-months. The ADA recommends testing in children with type 1 diabetes at puberty or after having diabetes for 5 years.
Early detection of microalbumin is important because it indicates increased risk for both renal and vascular disease. Fortunately, early detection allows for treatments that may delay the beginning of a more serious disease.
If you have diabetes, you have a higher risk of heart and blood vessel disease (cardiovascular disease). One way to limit this risk is to measure your cholesterol routinely and control it by changing your lifestyle or taking prescription drugs. A cholesterol test usually shows your total cholesterol, total triglycerides, and high-density lipoproteins (HDLs). The Centers for Disease Prevention and Control (CDC) has set up a National Reference System for Cholesterol Testing and many manufacturers verify their test through certification with this method.
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