Time below range of 70 mg/dL can be used to estimate lower cutoff in type 1 diabetes
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A strong correlation exists between time below range of 54 mg/dL and time below range of 70 mg/dL, though the difference between the two values varies based on continuous glucose monitoring type, according to study data.
In a study published in Diabetes Technology & Therapeutics, researchers analyzed data from Dexcom CGM devices used in nine type 1 diabetes trials to analyze the relationship between time below of less than 70 mg/dL vs. 54 mg/dL. The ratio between the two cutoffs widened as time with a glucose level of less than 70 mg/dL increased, and the ratio was larger for participants using a masked CGM vs. those using an unmasked CGM or automated insulin delivery system.
“In clinical care, it is more important to avoid glucose levels dropping to less than 54 mg/dL than to less than 70 mg/dL as the lower level is associated with a number of adverse effects, such as cognitive impairment and increased risk of cardiac arrhythmias and a severe hypoglycemia event,” Roy W. Beck, MD, PhD, president and medical director of the Jaeb Center for Health Research Foundation, told Healio. “Certain reports of CGM data may only show time less than 70 mg/dL, and in such cases, the time with less than 54 mg/dL can be estimated from the ratios reported in this paper.”
Researchers obtained data from 886 people with type 1 diabetes who participated in a clinical trial using a Dexcom CGM. Masked CGM data were available for 599 participants (92 children, 507 adults), unmasked CGM data were obtained from 682 participants (148 children, 534 adults), and automated insulin delivery system data were available for 190 participants (109 children, 81 adults). Time below ranges of less than 70 mg/dL and less than 54 mg/dL were calculated with at least 240 hours of CGM data for the masked period and at least 336 hours of data for unmasked and automated insulin delivery periods. Researchers calculated the overall ratio between time below range of 70 mg/dL and time below range of 54 mg/dL, as well as ratios for different types of device use.
Regardless of the type of device used, the time below range 54 mg/dL to 70 mg/dL ratio increased as time below range of 70 mg/dL increased. The ratio was higher with masked CGM compared with unmasked CGM and automated insulin delivery.
With masked CGM, the time below range ratio varied from 19% when the time below range of 70 mg/dL was less than 1% to 44% when the time below range of 70 mg/dL was 7% or higher. For unmasked CGM, the ratio ranged from 15% with a time below range of 70 mg/dL of less than 1% to 42% with a time below range of 70 mg/dL of 7% or higher. When time below range of 70 mg/dL was 4%, the predicted time below range of 54 mg/dL was 1.18% for masked CGM, 0.94% for unmasked CGM and 0.91% for automated insulin delivery (P < .001).
“Prior to doing the analysis, we were not aware that the ratio of time less than 70 mg/dL to time less than 54 mg/dL varied according to whether a blinded CGM sensor was being used or real-time CGM,” Beck said. “The finding that it does vary makes sense.”
For more information:
Roy W. Beck, MD, PhD, can be reached at rbeck@jaeb.org.
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