Clinical Limitations of the Relationship Among Mean SMBG, CGM and HbA1c

Year: 2008
Abstract Number: 45-OR
Authors: ROGER MAZZE, ELLIE STROCK, DAVID WESLEY, ROBERT M. CUDDIHY, Minneapolis, MN
Institutions: Minneapolis, MN

Results: Although it is known that HbA_1c is associated with summary measures of glucose exposure, its relationship to biologically and clinically relevant diurnal glucose patterns remains ambiguous. We hypothesized that summary SMBG and continuous glucose monitoring (CGM) measures, while associated with HbA_1c, are insufficient to represent variation in diurnal glucose patterns. Ambulatory Glucose Profile (AGP) analysis was employed to graphically (see Figure 1) and statistically (see Table 1) represent: (1) exposure - area under the median curve (AUC); (2) variability - inter-quartile range (IQR)); and, (3) stability - % hypo - and hyperglycemia, and average absolute hourly rate of change in the median curve.
Sixty-two subjects with HbA_1c 6.4±1.3% (range 5-9.2%), SMBG 133±37 mg/dL and CGM 129±37 mg/dL, monitored for 30 days producing 3214±572 CGM and 92±81 SMBG tests. Mean SMBG and CGM were correlated with HbA_1c, R²=0.81, P<0.001 and R²=0.86, P<0.000001, respectively. Since SMBG was too episodic to represent diurnal glucose patterns, only CGM was used to graphically display and test the relationship between glucose exposure, variability, stability, and HbA_1c. Only percent hypoglycemia (<70 mg/dL) was not associated with HbA_1c (Table 1). To determine hypoglycemia’s significance, six subjects with > 10% hypoglycemia were compared to 14 with < 1 %. Although the first group averaged 11±0.8% and the second 0.3±0.3% hypoglycemia, there was no significant difference between CGM (135±39 vs.137±44 mg/dL) and HbA_1c (6.7±1.5% vs. 6.4±1.3%). Individual AGPs, however, revealed clinically significant differences in diurnal patterns (Figure 1).
Therefore, without diurnal glucose profiles the clinical and biological relevance of HbA_1c or related summary measures are insufficient for clinical decision-making.
[table1][figure1]

Category: Clinical Therapeutics/New Technology - Glucose Monitoring and Sensing

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