Steve V. Edelman, MD
Robert R. Henry, MD
Self-Monitoring of Blood Glucose (SMBG) Systems
A combination of factors affect the overall performance of SMBG systems…
Analytic error can range from 4% to 33%; a goal of future SMBG systems is an analytic error of ± 5%. User performance is most affected by the quality and extent of training, which currently is hindered by reimbursement policies for diabetes education. Initial and regular assessments of a patient’s SMBG technique are necessary to assure accurate results. Patients need to be advised that test strips can be adversely affected by environmental factors. In addition, cautious use of generic test strips is warranted because of the complex process of calibrating test strips to specific meters.
Examples and features of available blood glucose meters are shown in Table 13.2. The ADA Consensus Panel advises periodic comparisons between a patient’s SMBG system and a sample obtained simultaneously and measured by a referenced laboratory. Remember that whole blood glucose values are generally 15% lower than plasma values.
Who Should Perform SMBG?
Virtually all patients with diabetes should perform SMBG because of the value of this evaluation tool in promoting improved glycemic control and reinforcing adherence to therapy. The frequency of SMBG is dictated by the complexity of the therapeutic regimen. For example, insulin-using type 2 diabetics (particularly those on an intensive regimen) would need to perform more daily SMBG evaluations than patients who are achieving acceptable glycemic control with diet, exercise, and oral agents.
Recommended Frequency of SMBG
The frequency of SMBG varies considerably based on the complexity of the therapeutic regimen and the clinical situation of the individual. In addition to guiding therapy, SMBG also has educational and motivational advantages. For example, intermittent measurements 1 to 2 hours after meals can provide an assessment of glycemic response to various types of foods, thus helping patients learn which foods have the greatest and least impact on blood glucose, as well as how the size of a meal affects glucose levels. SMBG also can help motivate patients (especially obese patients trying to lose weight), because they can observe immediate decreases in their blood glucose levels in response to dietary modifications, exercise, and oral therapy.
Patients who demonstrate consistent, acceptable glucose results may require fewer tests (i.e., one to three tests per week). However, testing requirements may increase when metabolic control worsens.
SMBG for Patients Who Do Not Take Insulin
Traditionally, SMBG was viewed as not necessary for type 2 patients on diet therapy or oral agents because glucose levels remained relatively stable on these treatment regimens. For these patients, SMBG was recommended only for monitoring short-term adjustments in therapy or for patients at risk for hypoglycemia. Because better glycemic control has been shown to be associated with a greater frequency of SMBG, this evaluation measure now is recommended for all patients, including those not taking insulin. The frequency of testing depends on how stable the patient is. Patients with less than optimal control should monitor their levels more frequently.
• 1 to 2 hours postdinner — two to three tests per week.
Monitoring glucose values from these two important time points, in addition to an A1C or fructosamine value every 3 to 6 months, is an efficient way to follow patients on diet and oral agents.
SMBG recommendations for patients using oral agents alone or combination therapy (daytime oral agents, evening insulin):
• 2 hours postdinner — two to three tests per week.
Patients in this category generally require one to three tests per day when SMBG values are consistent. Patients can make nonpharmacologic changes in their diabetic regimen depending on the results (Table 13.3).
• Increase the time interval between insulin injection and consumption of the meal.
• Eliminate or replace foods containing refined carbohydrates or that have a high glycemic index, such as fruit exchanges.
• Make the appropriate long-term adjustment in preceding insulin dose to prevent hyperglycemia at a particular time if a consistent trend is identified.
SMBG for Patients Who Take Insulin
SMBG is critical for all patients who take exogenous insulin, particularly those on intensive insulin regimens or on combination therapy. The type of insulin regimen used should dictate the frequency of SMBG, with attention to insulin pharmacokinetics and the timing of insulin injections. The best time to evaluate the effectiveness of a dose is at the peak time of action of a particular type of insulin.
Frequent SMBG is necessary to fine-tune an insulin regimen to the needs and responses of a given patient. Ideally, SMBG should be performed four to six times per day (before each meal, at bedtime, and occasionally after meals and at 3 AM, which is the approximate time of early morning glucose nadir). A more intensive SMBG schedule would be a preprandial and 2-hour postprandial measurement and at bedtime, depending on the frequency of insulin doses.
• One injection per day — two tests per day; no less than one to three depending on metabolic control.
• Two injections per day — four tests per day (before each meal and at bedtime)
• Intensive regimen (multiple injections, external pump) — four to seven tests per day.
Results should be recorded in a logbook that is brought to each office visit so the physician can evaluate the effectiveness of the insulin regimen and determine the most appropriate insulin dosage adjustments. Selected patients should be instructed to apply their SMBG results as the data become available. Making immediate dosage adjustments based on SMBG feedback is evidence of the true benefit of this self-assessment tool.
Additionally, most meter logs can be downloaded directly to a personal computer.
When SMBG reveals premeal hyperglycemia, a number of different methods can be used in addition to adjusting the dose of insulin to reduce daily glycemic excursions (Table 13.3).
Next Week: Applying SMBG Results to Adjust Insulin Doses and Advances in glucose Monitoring
You can purchase this text at Amazon.com, just click on this link: Diagnosis and Management of Type 2 Diabetes 10E
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Buckingham B, Caswell K, Wilson DM. Real-time continuous glucose monitoring. Curr Opin Endocrinol Diabetes Obes. 2007;14:288-295.
Fleming DR. Accuracy of blood glucose monitoring for patients: what it is and how to achieve it. Diabetes Educ. 1994;20:495-500.
© Copyright 2010. Steven V. Edelman, MD, Robert R. Henry, MD, Professional Communications, Inc. All rights reserved.