Response to “Blood Glucose Monitoring Data Should Be Reported in Detail When Studies About Efficacy of Continuous Glucose Monitoring Systems Are Published”

Pleus et al ¹ have shown in a recent issue of Journal Diabetes Sciences and Technology that patients seemed to spend considerably less time in hypoglycemia in two studies which used real-time blood glucose monitoring (RTBGM)^2,3 than in one study which used interstitial continuous glucose monitoring (ICGM), ⁴ that is FreeStyle Libre CGM (FSL-CGM). They suggested that ICGM or RTBGM data should not be reported without accompanying BGM and that quantitative analysis of the bias between ICGM and BGM should be done. We have already reported and quantified, using FSL-CGM, the bias between ICGM and BGM data in insulin-treated dependent elderly people with diabetes living in a long-term care home. Out of 144 interstitial glucose (IG) lower than 70 mg/dL, 74 (51.4%) were associated with blood glucose (BG) equal or higher to 70 mg/dL. In our group of false hypoglycemia, IG was significantly lower than BG (56.8 ± 8.7 vs 89.6 ± 15.6 mg/dL, P < .0001, Wilcoxon paired test). Mean IG was also significantly lower than BG in the 70-180 mg/dL BG group and did not differ from BG in the >180 mg/dL BG group. This resulted in a mean absolute difference of 10.6 and 27.3 mg/dL for the <70 and 70-180 mg/dL range, respectively, and a mean absolute relative difference of 18.0% (95% CI 14.2-21.8%) and 25.5% (95% CI 22.7-28.3%) for the <70 and 70-180 mg/dL range, respectively. ⁵ Therefore, FSL-CGM could not be suitable for the detection of hypoglycemia which is a major issue in this population. Interestingly, the FDA explicitly noted in its premarket approval that FSL-CGM may inaccurately indicate hypoglycemia because in 40% of cases in which sensor glucose readings were <60 mg/dL (< 3.3 mmol/L), BGM were in the range of 81 to 160 mg/dL (4.5 to 8.9 mmol/L). ⁶ Improvement of FSL-CGM performance in the low and middle IG range is clearly needed for reliable detection of hypoglycemia and better evaluation of diabetes control.