Oral Presentation Hypoglycaemia

Detection of unseen hypoglycemia using continuous glucose monitoring

Todd M. Gross, Ph.D., John J. Mastrototaro and Linda P. Fredrickson
MiniMed Inc., Sylmar, CA, U.S.A.

Tight control of blood glucose levels currently offers the best chance of reducing the long-term complications of diabetes mellitus [1]. However, attempts to maintain near-normal glycemia often increase the risk of hypoglycemia [2]. Although patients may perform self-monitored blood glucose (SMBG) tests four or more times per day, many episodes of hypoglycemia go undetected due to the absence of overt symptoms or because they occur at night, when glucose testing is rare. As a result, hypoglycemia is responsible for dramatic economic costs and many avoidable deaths each year.

A continuous glucose monitoring system
In order to capture asymptomatic hypoglycemia with traditional SMBG, one must either accurately predict when it occurs (based on patient history) or perform SMBG at an impractical frequency (i.e. every 15 min). With the recent advent of a commercially available continuous glucose monitoring system (CGMS; MiniMed Inc., CA, USA), detecting low blood glucose is straightforward. Simply insert the sensor, turn on the monitor and have the patient go about his or her normal daily and nightly routine. The data collection is passive and requires only that patients enter at least three daily SMBG values into the monitor.
Through the use of this new technology, the true incidence of low blood glucose is revealed. The resulting information allows clinicians to identify the time and duration of hypoglycemic events, recommend therapy changes to address these events and confirm the effect of these changes with follow-up sensor use. Clinicians and researchers alike can now capture hypoglycemia whenever it occurs and tailor research and treatment protocols accordingly. Such an exploration is the first step in reducing the most dramatic acute side effect of intensive diabetes management.
Continuous monitoring has already been proven reliable and effective in guiding treatment [3, 4].

Figure 1: The components of the MiniMed® Continous Glucose Monitoring Systems (CGMS).

 The MiniMed CGMS (Fig. 1) utilizes a subcutaneous sensor, connected by a thin cable to a pager-sized monitor [5]. The monitor stores an average value every 5 min, for 288 readings each day. Once the CGMS software retrospectively calibrates and graphs these readings, the continuous profiles can be reviewed and episodes of hypoglycemia readily identified (Fig. 2). Of particular value are the detailed patterns obtained following meals and at night.

Figure 2: Daily Glucose Profile from the MiniMed Continuous Glucose Monitoring Ssytem (CGMS) showing episodes of nocturnal and post-insulin hypoglycemia.

Superior results with CGMS vs. SMBG
Study results presented at the 36th annual meeting of the EASD confirm the ability of the CGMS to capture episodes of hypoglycemia. In this study, the continuous glucose profiles and SMBG values of 238 patients, from 13 clinical centers, were reviewed for blood glucose readings below 3.3 mmol/l (60 mg/dl). Subjects used the CGMS at their physicians’ direction and according to its instructions for use.

Table I. Comparison of hypoglycemic detection based on continuous glucose monitor data (MiniMed’s CGMS) or periodic meter testing (SMBG).

As seen in Table I, the CGMS revealed a startling degree of hypoglycemia. Based on the CGMS, 87% of subjects had at least one hypoglycemic event in the 3 days of sensor use. The average subject experienced 1.8 events in 24 h, with 0.6 of these events occurring between 2200 and 0600 h. Each event lasted on average 72 min. In contrast, SMBG readings showed only 55% of the subjects with any hypoglycemia during the same period, with an average of less than 0.4 events in 24 h and 0.1 nocturnal events. Further, the average duration of hypoglycemia cannot be derived from SMBG readings. Of greatest import, the CGMS revealed 1.4 events per 24 h that were not detected by a concurrent fingerstick.
Continuous glucose monitoring is an essential tool in the fight to remove the most fearful acute complication of diabetes therapy. Even among patients who are practicing frequent blood glucose testing, up to 75% of hypoglycemic events may go undetected. SMBG readings alone underestimated the incidence of hypoglycemia, particularly at night, thus confirming the clinical benefit of the CGMS to detect previously unrecognized hypoglycemia. Use of the CGMS will allow clinicians to accurately diagnose a patient’s risk of hypoglycemia and to make informed treatment modifications.

References
1. The Diabetes Control and Complications Trial Research Group. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. N Engl J Med 1993; 329(14): 977–86. 
2. Diabetes Control and Complications Trial. Diabetes 1997.
3. Gross TM et al. Diabetes Tech Ther 2000.
4. Bode BW, Gross TM, Thornton KR, Mastrototaro JJ. Continuous glucose monitoring used to adjust diabetes therapy improves glycosylated hemoglobin: a pilot study. Diabetes Res Clin Pract 1999; 46(3): 183–90.
5. Mastrototaro J. The MiniMed continuous glucose monitoring system (CGMS). J Pediatr Endocrinol Metab 1999; 12 (suppl 3): 751–8.

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