Hemoglobin A1c Values and CGM

Dear Editor:

T he study by Pepper et al. ¹ compares hemoglobin A1c values in 102 patients with type 1 or 2 diabetes from up to 6 months before to 1.5–7 months after a 3-day blinded use of professional continuous glucose monitoring (CGM) (iPro™; Medtronic, Northridge, CA). The study's retrospective nature, lack of specific time periods for hemoglobin A1c assessments, and lack of description as to how the CGM data were used raise concerns about its conclusions.

The study fails to reveal how the CGM data were interpreted and used. There was no analysis with regard to treatment recommendations and adherence to those recommendations in the study report. The lack of clear standardization of the data analysis and lack of information about how the CGM data were used raise questions about the validity of the study conclusion.

Including hemoglobin A1c values that were collected up to 6 months before and as soon as 1.5 months and as long as 7 months after the subject used iPro makes the hemoglobin A1c outcomes difficult to interpret. I would like to see the hemoglobin A1c data on the patients who had an A1c level measured in the 1–2 weeks prior to the CGM and 3–4 months after the CGM.

A prospective design with standardized intervals between hemoglobin A1c measurements may have strengthened the study, as would additional details on results of the iPro studies and subsequent recommendations and behavioral changes (if any).

Short-term CGM studies remain a valuable tool for discovery and discussion of glycemic excursions and trends in people with diabetes.