Limitations of Reporting Time Below Range as a Percentage

Continuous glucose monitoring (CGM)-based metrics such as time in range and time below range (TBR) and their clinical targets are recommended along with glycated hemoglobin (A1c) to optimize diabetes care. CGM metrics are easy to understand by people with diabetes and have been widely accepted among health care providers. TBR, that is, time spent below a certain glucose level (e.g., <70 mg/dL and <54 mg/dL), is expressed as a percentage. This brief report draws attention to some limitations of TBR when expressed as an integer percentage and highlights problems introduced by rounding-off of numerical values for TBR on ambulatory glucose profile and other reports from CGM and automated insulin delivery systems that may be misleading or incorrectly interpreted. The goal of this article is to generate more discussion around reporting of TBR in ways that can be clinically impactful for people living with diabetes, health care providers, regulatory agencies, and payers to stratify and predict severe hypoglycemic events.