Blood Glucose Monitors

US Pharm. 2006;31(11)(Diabetes suppl):7-12.

Until the mid-1970s, patients with diabetes who sought to determine the percentage of glucose in the blood were able to do so only through using sticks or tablets to test urine (e.g., Clinistix, Clinitest, Tes-Tape, Diastix). The advent and widespread acceptance of blood glucose monitors (meters) in the mid-1970s revolutionized control for patients with diabetes.¹ The American Diabetes Association now recommends self-monitoring of blood glucose (SMBG) to help ensure tight control of the condition.² Since their inception, blood glucose meters have undergone numerous changes, each designed to make them more user-friendly and increase their utility.

The Rapidly Changing Nature of the Market
Blood glucose monitors appear to be small, uncomplicated devices. However, they are extremely intricate machines that use the latest technological advances to provide an accurate measure of blood glucose levels. Manufacturers of these products have historically been extremely responsive to changes in design. As soon as one manufacturer develops an innovative and useful new feature for its monitors, other companies must analyze the innovation to determine whether it is worth emulating. Thus, manufacturers can gain a competitive advantage by continually updating their product line to attract purchasers. As a result of this rapidly changing market, blood glucose meters experience an obsolescence virtually unprecedented among devices sold in pharmacies. A meter that is state-of-the-art in 2007 may be hopelessly outdated by 2008.

Competition and Profit
A major factor driving the rapid changes in the blood glucose monitor market is a result of the enormous profits attendant upon their purchase and continued use. However, the cost of the meters themselves is actually a minor point for the manufacturers. In fact, some manufacturers virtually give the meters to patients for free by offering partial or total rebates on their purchase. The reason for this seeming generosity lies in the profitability of the blood glucose strips that must be used with the meters. Each meter requires its own strip. Indeed, this strip requirement is so specific that when a blood glucose meter becomes obsolete, its test strips often become difficult or impossible to locate, eventually forcing the patient to purchase a new meter.

The cost of blood glucose testing strips is the real issue behind the dynamic nature of the blood glucose testing market. Depending on the purchase location, a box of 50 blood glucose test strips may sell for $30 to $40, while a box of 100 strips may retail for $60 to $75.

The American Diabetes Association estimates that there are 20.8 million children and adults with diabetes--approximately 7% of the population.³ At least 5% to 10% of all people with diabetes have type 1 diabetes.⁴ Another 135,000 cases of gestational diabetes occur each year. The balance is a large number of patients with type 2 diabetes. While the role of SMBG for patients with stable type 2 diabetes that is treated only by diet is undefined, some argue that it would be beneficial.⁵

The typical patient with type 1 diabetes may test three to four times a day or more (e.g., before meals, two hours after meals, at bedtime, at 3 a.m., and any time the patient experiences signs or symptoms).⁵ This translates to an annual strip cost of $1,100 to $1,150. The typical patient with type 2 diabetes may test only once or twice daily, for an annual strip cost of $270 to $600.⁶ Patients with gestational diabetes are usually advised to test twice daily.⁵ Thus, a manufacturer that markets a blood glucose monitor that is better accepted than others stands to gain hundreds of millions of dollars in income, given that the annual SMBG market is estimated at several billion dollars. ⁵

Even though physicians and national organizations have provided well-defined recommendations for SMBG testing frequency, research has confirmed that there is a wide gap between the recommendations and the actual practice of patients.⁷ This is largely due to the expense of the strips, a concern that may be alleviated if manufacturers would cooperate to produce monitors that all accept the same low-cost generic strip. As the realities of competition will likely prevent this utopian ideal from coming to fruition, pharmacists will continue to confront questions surrounding strip purchases and the attendant expenses. At one time, patients resorted to purchasing razor-like devices known as strip splitters, which purportedly allowed them to split the strip in half lengthwise, effectively halving the cost of strips. Monitor manufacturers discouraged patients from this practice, asserting that the accuracy of the devices could not be guaranteed under those circumstances.

Literature on Blood Glucose Meters
I t is difficult for pharmacists to find articles about blood glucose meters that are completely up-to-date. Although an author may obtain the most current information available at the time of writing an article, new meters may appear on the market during the typical lag time of several months between submission of a manuscript and its publication. Thus, pharmacists should continually scan the shelves to ascertain which models are most current. Manufacturer Web sites, which are updated frequently, provide a good overview of the current products. Furthermore, advertisements in pharmacy journals often highlight the latest meters.

The Importance of Counseling
Blood glucose monitors are complicated, as a brief look at their instruction manuals demonstrates. For this reason, the patient with diabetes should be urged to obtain training in meter use from a certified diabetes educator (CDE). As part of a comprehensive diabetes-training program, the CDE should demonstrate the meter and have the patient use the meter under his or her close supervision. ⁵ The National Certification Board for Diabetes Educators provides details about the process of CDE credentialing at www.ncbde.org/about.html. However, even a pharmacist who is not a CDE still fields many questions about meters and strips.

Pharmacists can provide general advice about monitor use. The patient should follow a standard set of steps, beginning with washing the hands with soap and warm water and cleansing the sample area with alcohol.⁵ After the sample area has dried, the patient should use the lancet to puncture the skin at the site indicated. The patient must next follow directions--required by the FDA for each meter and strip set--for inserting the strip and using the meter. Patients should read all of the instructions prior to first use and keep them for future reference.

Patients should bring their monitor with them to all counseling sessions, whether the session is conducted by a physician or a CDE. The pharmacist or counselor can watch and critique the patient's use of the device. Further, the patient can also have a blood sample analyzed by both a laboratory and his or her own meter. If the laboratory and the meter agree, the meter and patient's technique can be trusted. If they do not, the pharmacist or CDE should examine the patient's technique and/or consult the meter's manufacturer.

Recent Innovations
Calibration Issues: Most glucose meters require preuse calibration.^7,8 This may consist of entering a calibration code or using a check strip. Apparently, many patients fail to perform this critical step correctly. Based on research demonstrating that 16% of patients carrying out SMBG use incorrectly coded meters, a group of researchers assessed the results of several intentionally miscoded meters. ⁸ They used blood samples from 50 subjects in two different meters. Each meter was miscoded using a number different from that recommended for the strip utilized. Incorrect coding produced results that differed from those of properly coded meters by as much as 30%. The investigators also tested a blood glucose monitor with an autocoding feature. Although the investigators attempted to use different strips to challenge this system, it did not display inaccuracies.

The first meter with the autocoding feature was the recently introduced Ascensia Contour, now joined by the Ascensia Breeze.⁹ Both use special test strips that eliminate the need for coding, as calibration occurs with each strip insertion.⁷ Of course, the advantage in using their unique strips is also a significant disadvantage for some users, as the strips are no less expensive than most other strips. The meters also carry the standard features included in the current generation of meters.

Meters can usually read blood glucose values ranging from 0 to 600 mg/dL. However, the FDA urges patients to interpret very high or low values with extreme caution.⁵ Patients might consider checking the calibration of the meter and confirming these values with an additional reading.

Sample Size Required: One of the disincentives to SMBG is the need to obtain blood samples. Older blood glucose meters (e.g., Accu-Chek Advantage) required 4 to 10 microliters of blood.¹⁰ Some even included instructions intended to maximize the sample volume, such as:
• Massage the hand from the wrist down to the fingertips several times to increase the volume of blood.
• Apply greater pressure to the finger with the bloodletting device to deepen the puncture wound.
• Massage the punctured digit to increase the amount of blood dripping onto the strip.

Unfortunately, users reported that the discomfort associated with blood withdrawal and the associated manipulations was directly proportional to the size of sample required by the meters. To help prevent this source of discomfort-associated noncompliance, manufacturers gradually decreased the sample size required by the meters. Sample sizes decreased to 1 microliter, then to 0.6 microliter, and now to 0.3 microliter. Most newly introduced meters require only 0.3 microliter. Eventually, manufacturers will undoubtedly reduce the required sample size further, spawning yet another generation of small-sample meters.

Some meters (e.g., Glucometer Dex 2) pull the blood sample into the meter through a capillary action, preventing the patient from having to insert the strip into the meter.

Ability to Sample from Other Areas: The finger has a rich blood supply that makes it a mandatory testing site for large-sample testing meters. Unfortunately, the fingers also have the nerves required for sensitivity of touch. Thus, repeated blood withdrawal produces pain or discomfort that endures throughout the day.

The introduction of meters that could process smaller sample sizes opened the possibility of sampling at sites other than the fingers. Using alternate sites reduces pain because the needle stick does not have to penetrate as deeply and there are fewer nerve endings at sites other than the fingers. For example, the older Accu-Chek Advantage requires a finger stick, but the newer Accu-Chek Aviva permits testing from the palm, forearm, upper arm, calf, or thigh.

The FDA has cautioned against using nonfingertip sites for SMBG.⁵ The agency has asserted that blood in the fingertips exhibits changes in blood glucose more rapidly than does blood in other sites. This could be crucial, as the alternate sites may not reflect the current level of blood glucose when it is undergoing a rapid change (e.g., following a meal, insulin administration, or exercise). The agency stated, "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."⁵ The agency requested that all manufacturers demonstrate that their device is not affected by differences between alternative site and fingertip blood samples during rapidly changing blood glucose situations or alert patients to the possibility of obtaining incorrect values at those times. The alert would also warn patients not to use alternative test sites if they think they are hypoglycemic, if they are not aware of symptoms when they experience hypoglycemia, or if alternate site results do not agree with their own perception of their blood glucose levels.

Testing Speed: The time required to obtain a result from the monitor could be critical in the case of a patient with severe hypoglycemia. Current meters produce results in as little as five to 30 seconds.

Cleaning: Some meters, especially the older versions, required regular cleaning with soap and water to maintain accuracy.⁵ Newer meters function without external cleaning, making them more convenient.

Quality Controls: Test solutions are often supplied with meters and are also available from pharmacies. These quality control checks help ensure the accuracy of meters, which may be dropped, immersed in water, or exposed to heat or extreme humidity. Patients substitute the test solutions for blood samples, following the same steps to produce a blood glucose measurement. They compare the results provided by the meter with the actual value of the control solution, ideally producing the measurement. If there is a discrepancy, the monitor is not working properly. Manufacturers also may include a cartridge or special control test strip that generates a signal if the meter is performing properly.

Other Features: Most blood glucose monitors store previous readings, including the time and date of the reading. The number of previous readings varies with the specific meter, from about 250 to as many as 3,000 (OneTouch UltraSmart). Most meters enable users to download readings directly to their home computer, although this feature sometimes requires special cables or software that can be downloaded from the meter manufacturer's Web site. The software may allow patients to obtain 14- and 30-day averages, as well as averages of all readings taken at any specific time (e.g., 6 a.m. or noon).

Monitors are powered by batteries, which are ideally readily available in any mass marketer and easy to replace. Although many meters fulfill this need, requiring only two common alkaline batteries of AA or AAA size, others require more expensive and difficult-to-locate lithium watch batteries or AAAA batteries. Patients should purchase two sets of batteries at a time, so a backup set will always be available. Meters usually yield 700 to 1,000 tests per battery set.

Some patients are directed to test ketones. For many years, patients had to use at-home urine ketone test strips. However, some blood glucose meters, such as the Precision Xtra, can also measure ketone levels. Each package of blood glucose strips also includes a few ketone test strips, along with strips to calibrate the meter for glucose and ketones.

The CheckMate Plus monitor has a useful feature: a built-in lancet. The patient applies 4.5 pounds of pressure to cock a lancet, places the target finger over a built-in finger bowl, and triggers the lancet. The drop of blood is applied to a wick on the test strip, and the results are read in 60 seconds.

Conclusion
Blood glucose monitors are complicated devices that are redesigned frequently. Patients benefit from an informed pharmacist who can help them understand the various features of the different meters prior to purchase of a specific model.

REFERENCES

1. Pray WS. Noncompliance with self-monitoring of blood glucose: the problem and possible solutions. The CE Solution. Available at: www.thecesolution.com/ce/index.asp. Accessed October 4, 2006.

2. Kimberly MM , Vesper HW, Caudill SP, et al. Variability among five over-the-counter blood glucose monitors. Clin Chim Acta. 2006;364:292-297.

3. American Diabetes Association. Total prevalence of diabetes and pre-diabetes. Available at: www.diabetes.org/diabetes-statistics/prevalence.jsp. Accessed October 4, 2006.

4. American Diabetes Association. All about diabetes. Available at: www.diabetes.org/aboutdiabetes.jsp. Accessed October 4, 2006.

5. FDA. Glucose meters & diabetes management. Available at: www.fda.gov/diabetes/glucose.html. Accessed October 4, 2006.

6. Sachon C, Jacqueminet S, Hartemann-Heurtier A, Grimaldi A. Should diabetic patients be asked to test their blood glucose 90 to 120 minutes after the beginning of their meals? Diabetes Metab. 2006;32:377-381.

7. Kilo C Sr, Dickey WT Jr, Joynes JO, et al. Evaluation of a new blood glucose monitoring system with auto-calibration for home and hospital bedside use. Diabetes Res Clin Pract. 2006;74:66-74.

8. Baum JM, Monhaut NM, Parker DR, Price CP. Improving the quality of self-monitoring blood glucose measurement: a study in reducing calibration errors. Diabetes Technol Ther. 2006;8:347-357.

9. Bayer HealthCare. Accuracy made easy. Available at: www.bayercarediabetes.com/prodserv/products/contour/index.asp. Accessed
October 4, 2006.

10. Walgreen Co. Blood glucose meter comparison chart. Available at: www.walgreens.com/library/centers/diabetes/bgmcc.jsp. Accessed October 4, 2006.

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