The Relationship Between CGM-Derived Metrics, A1C, and Risk of Hypoglycemia in Older Adults With Type 1 Diabetes

Abstract

Continuous glucose monitoring (CGM) is now commonly used in the management of type 1 diabetes (T1D). The CGM-derived coefficient of variation (CV) measures glucose variability, and the glucose management indicator (GMI) measures mean glycemia (previously called estimated A1C). However, their relationship with laboratory-measured A1C and the risk of hypoglycemia in older adults with T1D is not well studied. RESEARCH DESIGN AND METHODSIn a single-center study, older adults (age ‡65 years) with T1D wore a CGM device for 14 days. The CV (%) and GMI were calculated, and A1C and clinical and demographic information were collected. RESULTSWe evaluated 130 older adults (age 71 6 5 years), of whom 55% were women, 97% were White, diabetes duration was 39 6 17 years, and A1C was 7.3 6 0.6% (56 6 15 mmol/mol). Participants were stratified by high CV (>36%; n 5 77) and low CV (£36%; n 5 53). Although there was no difference in A1C levels between the groups with high and low CV (7.3% [56 mmol/mol] vs. 7.3% [53 mmol/mol], P 5 0.4), the high CV group spent more time in hypoglycemia (<70 mg/dL and £54 mg/dL) compared with the group with low CV (median 31 vs. 84 min/day, P < 0.0001; 8 vs. 46 min/day, P < 0.001, respectively). An absolute difference between A1C and GMI of ‡0.5% was observed in 46% of the cohort. When the A1C was higher than the GMI by ‡0.5%, a higher duration of hypoglycemia was observed (P 5 0.02). CONCLUSIONSIn older adults with T1D, the use of CGM-derived CV and GMI can better identify individuals at higher risk for hypoglycemia compared with A1C alone. These measures should be combined with A1C for better diabetes management in older adults with T1D.Older adults with type 1 diabetes (T1D) are at a higher risk of hypoglycemia and its associated negative consequences, such as loss of consciousness, cardiac arrhythmias, traumatic falls, and higher risk of mortality (1-5). Current guidelines for older adults with T1D recommend less stringent hemoglobin A 1c (A1C) targets to mitigate hypoglycemia (6). However, studies have shown that liberalization of A1C may not protect against the risk of hypoglycemia in the older population (1,7-9). Additionally, comorbidities that affect red blood cell (RBC) life span, such as anemia, chronic kidney

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“…To date, numerous studies have been published on the relationship between CGM-related metrics and HbA1c 11 , 13 . However, most studies have been based on data extracted from published trials or articles for other purposes and does not exist as studies specified in measurement terms, to investigate for CGM data for a sufficiently long period of time 11 , 13 , 18 . To exactly investigate the relationship between HbA1c and CGM-related metrics, the measurement periods were fixed as 120, 90, 60, 30, and 7 days from the baseline.…”

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“…. However, studies have shown that liberalization of A1C may not protect against the risk of hypoglycemia in the older population" (15). Exactly!…”