Objective: Although developed to be a management tool for individuals with diabetes, continuous glucose monitoring (CGM) also has potential value for the assessment of outcomes in clinical studies. We evaluated using CGM as such an outcome measure.
Research design and methods: Data were analyzed from six previously completed inpatient studies in which both CGM (Freestyle Navigator™ [Abbott Diabetes Care, Alameda, CA] or Guardian(®) [Medtronic, Northridge, CA]) and reference glucose measurements were available. The analyses included 97 days of data from 93 participants with type 1 diabetes (age range, 5-57 years; mean, 18 ± 12 years).
Results: Mean glucose levels per day were similar for the CGM and reference measurements (median, 148 mg/dL vs. 143 mg/dL, respectively; P = 0.92), and the correlation of the two was high (r = 0.89). Similarly, most glycemia metrics showed no significant differences comparing CGM and reference values, except that the nadir glucose tended to be slightly lower and peak glucose slightly higher with reference measurements than CGM measurements (respective median, 59 mg/dL vs. 66 mg/dL [P = 0.05] and 262 mg/dL vs. 257 mg/dL [P = 0.003]) and glucose variability as measured with the coefficient of variation was slightly lower with CGM than reference measurements (respective median, 31% vs. 35%; P<0.001).
Conclusions: A reasonably high degree of concordance exists when comparing outcomes based on CGM measurements with outcomes based on reference blood glucose measurements. CGM inaccuracy and underestimation of the extremes of hyperglycemia and hypoglycemia can be accounted for in a clinical trial's study design. Thus, in appropriate settings, CGM can be a very meaningful and feasible outcome measure for clinical trials.