Blood Glucose Monitoring Overview

Blood glucose fluctuations are a source of major morbidity and mortality in diabetes. The Diabetes Control and Complications Trial (DCCT) and the United Kingdom Prospective Diabetes Study (UKPDS) demonstrated that limiting hyperglycemia can reduce the risk for a variety of diabetic complications.[1,2] However, when blood glucose is tightly controlled, there is an increased risk of hypoglycemia, especially among insulin-requiring patients. The incidence of severe hypoglycemia requiring emergency assistance occurs at a rate of approximately 12 events per 100 patients per year for patients with type 1 diabetes and insulin-treated patients with type 2 diabetes.[3,4] Further, as few as 2 hypoglycemic incidents per week can reduce a patient's ability to detect future hypoglycemic episodes.[5] Accordingly, self monitoring of blood glucose (SMBG) in order to detect glycemic fluctuations is a critical component of diabetes self-management.

SMBG recommendations

The American Diabetes Association (ADA) recommends that patients with diabetes attempt to achieve and maintain glycemic levels that are as close to normal as is safely possible.[6] In order to achieve this goal, patients using insulin or insulin secretagogues should perform SMBG daily to detect asymptomatic hypoglycemia. An SMBG plan should be personalized to each individual patient, but patients with type 1 diabetes should perform SMBG at least 3 or more times daily. SMBG among people with type 2 diabetes is still a contested issue, but it should be used to ensure that glycemic targets are met. Frequency of SMBG may be increased when changes to treatment are being implemented.

In terms of adherence with these recommendations, patients with diabetes fall well below the recommended rate of SMBG, with fewer than 50% of patients with diabetes performing SMBG at least once daily.[7] There are numerous barriers to performing SMBG, with pain and inconvenience being among the more commonly reported barriers. One study demonstrated that a variety of other factors, such as lower socioeconomic status (SES), older age, fewer comorbities, obesity, and African American race, were associated with less frequent monitoring.[8] Cost of monitoring may also be an important barrier, as higher out-of-pocket costs for SMBG supplies was associated with decreased levels of SMBG.[9] Conversely, providing patients with access to supplies was associated with increased SMBG and improved A1C.[10]

Effectiveness of SMBG

Effectiveness of SMBG depends on several factors, including accuracy of technique and accuracy of data interpretation.[6] Inaccuracy of SMBG technique is a widespread problem, with one study demonstrating that nearly 20% of participants had SMBG test results that fell outside the acceptable 15% limit for meter accuracy when compared with a control test.[11] Common sources of error included lack of periodic meter technique evaluation, incorrect use of control solution, lack of hand washing, and unclean meters. Recommendations to improve SMBG accuracy appear in Table 1. Once SMBG values have been obtained, the next challenge facing patients is interpretation of the data. Patients must use SMBG data to manage food intake, physical activity, and pharmacologic therapy.[6]

Table 1. Recommendations to improve SMBG accuracy[11]

Although SMBG is an integral part of self-management for insulin-requiring patients, the issue of efficacy and cost-effectiveness of SMBG for type 2 patients not treated with insulin remains equivocal. A recent review of SMBG among type 2 patients not on insulin identified 2 studies that showed a positive effect of SMBG on glycemic control.[12] However, other studies have failed to demonstrate an effect of SMBG on glycemic control among patients not using insulin.[13,14]

Blood glucose monitors

In order to meet the varying needs of people with diabetes, a variety of monitors exist. Monitors vary on a variety of criteria, including cost, accuracy, ease of use, level of maintenance required, portability, test time, test site, and ability to interact with data management software.[15] Some monitors require smaller amounts of blood than others, and some offer the ability to test on sites other than the tips of the fingers, although alternate site testing may not be as accurate as fingertip testing, especially in the postprandial period.[16] Some meters have the ability to load multiple test strips at one time for ease of use. Meter accuracy may decrease over time and should be checked at least monthly. A list of monitors and their features appears in Table 2.

Table 2. Blood glucose monitors and their features

*These are test strips approved by the manufacturers. In some cases, manufacturers cannot guarantee results or provide assistance if any other test strips are used.

Continuous glucose monitoring

Although SMBG is a valuable tool for diabetes self-management, it only allows for discrete measurements and may miss asymptomatic blood glucose fluctuations. Accordingly, new technological innovations allow patients to monitor their glucose levels continuously using minimally invasive or noninvasive techniques. Most devices require a warm-up and calibration period. Following that period, the minimally invasive technique of continuously measuring interstitial fluid allows patients to measure glucose levels every 1-10 minutes for up to 72 hours. The noninvasive technique of applying electromagnetic radiation through the skin to the blood vessels can provide glucose readings for a period of up to 3 months.[17] Use of continuous glucose monitors (CGMs) is not suitable for every patient. The ideal patient to use a CGM is motivated to perform self-care tasks, knowledgeable about diabetes, and mechanically inclined.[17] Patients using CGMs should be trained to calibrate and operate the device. Further, in order to effectively interpret and use the vast amount of data the CGMs provide, patients must be extensively educated on safe and effective treatment decisions.

Use of CGMs offers a number of advantages over traditional monitoring, including reductions in A1C and better detection of postprandial glycemic peaks.[18] Specific clinical indications for the use of CGMs include periods of therapy adjustment, tightening glycemic control with decreased risk of hypoglycemia, diagnosing and preventing asymptomatic hypoglycemia, and diagnosing and preventing postprandial glucose fluctuations. CGMs are also benefical research tools, as they can be used to determine the effect of a particular pharmacologic therapy or lifestyle intervention.[17] The CGM devices also feature an alarm function that alerts the user to unsuspected hypoglycemia (eg, while sleeping). CGMs are improving in accuracy, with the second generation devices performing more accurately than their first generation predecessors.[17]

Conclusion

Blood glucose monitoring is an important component of diabetes self-management for patients using insulin and insulin secretagogues, although the optimal use of SMBG among other patients with diabetes is still being studied. Blood glucose monitoring allows patients to determine the presence of and treat glycemic fluctuations. Improvements in glucose monitoring technology include smaller monitors, monitors that allow for testing in a variety of different locations, monitors that do not require test-strip insertion at every use, and continuous monitoring devices. With all of these tools, motivated and educated patients can better manage their disease.

References

1. The Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications Research Group. Retinopathy and nephropathy in patients with type 1 diabetes four years after a trial of intensive therapy. N Engl J Med. 2000;342:381-389.
2. UKPDS Study Group. The effect of intensive blood-glucose control with sulphonylureas or insulin compared with conventional treatment and risk of complications in patients with type 2 diabetes. Lancet. 1998;352:837-853.
3. The Diabetes Control and Complications Trial Research Group. Hypoglycemia in the diabetes control and complications trial. Diabetes. 1997;46:271-286.
4. Leese GP, Wang J, Broomhall J, et al for the DARTS/MEMO Collaboration. Frequency of severe hypoglycemia requiring emergency treatment in type 1 and type 2 diabetes. Diabetes Care. 2003;26:1176-1180.
5. Ovalle F, Fanelli CG, Paramore DS, Hershey T, Craft S, Cryer PE. Brief twice-weekly episodes of hypoglycemia reduce detection of clinical hypoglycemia in type 1 diabetes. Diabetes. 1998;47:1472-1479.
6. American Diabetes Association. Tests of glycemia. Diabetes Care. 2004;27(suppl 1):S91-S93.
7. Centers for Disease Control and Surveillance. Levels of diabetes-related preventive care practices: United States, 1997-1999. MMWR. 2000;49:954-958.
8. Adams AS, Mah C, Soumerai SB, Zhang F, Barton MB, Ross-Degnan D. Barriers to self-monitoring of blood glucose among adults with diabetes in an HMO: a cross sectional study. BMC Health Serv Res. 2003;3:6. Available at: http://www.biomedcentral.com/content/pdf/1472-6963-3-6.pdf.
9. Karter AJ, Ferrara A, Darbinian JA, Ackerson LM, Selby JV. Self-monitoring of blood glucose: language and financial barriers in a managed care population with diabetes. Diabetes Care. 2000;23:477-483.
10. Nyomba BLG, Berard L, Murphy LJ. Facilitating access to glucometer reagents increases blood glucose self-monitoring frequency and improves glycemic control: a prospective study in insulin-treated diabetic patients. Diabetic Med. 2003;21:129-135.
11. Bergenstal R, Pearson J, Cembrowski GS, Bina D, Davidson J, List S. Identifying variables associated with inaccurate self-monitoring of blood glucose: proposed guidelines to improve accuracy. Diabetes Educator. 2000;26:981-989.
12. Welschen L, Bloemendal E, Nijpels G, et al. Self-monitoring of blood glucose in patients with type 2 diabetes who are not using insulin. Cochrane Database Syst Rev. 2005;CD005060.
13. Wen L, Parchman ML, Linn WD, Lee S. Association between self-monitoring of blood glucose and glycemic control in patients with type 2 diabetes mellitus. Am J Health-Sys Pharm. 2004;61:2401-2405.
14. Davidson MB, Castellanos M, Kain D, Duran P. The effect of self monitoring of blood glucose concentrations on glycated hemoglobin levels in diabetic patients not taking insulin: a blinded, randomized trial. Am J Med. 2005;118:422-425.
15. American Diabetes Association. Resource guide 2005: blood glucose meters and data management systems. Available at: http://www.diabetes.org/rg2005/meters.jsp. Accessed June 1, 2005.
16. Ellison JM, Stegmann JM, Colner SL, et al. Rapid changes in postprandial blood glucose produce concentration differences at finger, forearm, and thigh sampling sites. Diabetes Care. 2002;25:961-964.
17. Klonoff DC. Continuous glucose monitoring: roadmap for 21st century diabetes therapy. Diabetes Care. 2005;28:1231-1239.
18. The Diabetes Research in Children Network (DirecNet) Study Group. Eight-point glucose testing versus the continuous glucose monitoring system in evaluation of glycemic control in type 1 diabetes. J Clin Endocrinol Metab. 2005;90:3387-3391.