Design: Multicentre longitudinal observational CGM cohort
Population: 1,028 adults with type 1 diabetes, 3,441 CGM profiles
Primary outcome: Three-year change in time in range and time below range by subgroup
Effect: CKD TIR improvement β 0.228 (P = 0.002); severe β-cell failure attenuated TIR gain β −0.119 (P = 0.025)

This Korean multicentre study followed 1,028 adults with type 1 diabetes through 3,441 CGM profiles over three years, comparing subgroups often assumed to do badly: older age, chronic kidney disease, severe beta-cell failure, higher BMI and high triglyceride-glucose index.

At baseline all these groups spent more time above 180 mg/dL. Over time, older adults improved time in range as much as younger adults and kept lower time below range (1.7% vs 3.5%). People with CKD improved time in range significantly without more hypoglycaemia. Severe beta-cell failure — essentially no residual C-peptide — was the exception: it limited both time-in-range gains and hypoglycaemia reduction, and carried more glycaemic variability.

Within every subgroup the spread was wide. The message is to set targets from the person's own CGM trajectory rather than from their category.

Do not assume older adults with type 1 diabetes will fail on CGM — they improved as much as younger adults.
In CKD, time in range can improve without extra hypoglycaemia; keep reviewing CGM data.
Measure C-peptide where available — severe beta-cell failure predicted smaller gains and more variability.
In people with no residual beta-cell function, prioritise hypoglycaemia protection, such as automated insulin delivery.
Set individual time-in-range targets from each person's trajectory, not from subgroup averages.

Why it matters

It challenges the assumption that older age and CKD mean CGM targets should be abandoned.

The statistics, in plain English

The β coefficients describe how much faster or slower time in range changed in each group than the reference; a positive β with P below 0.05 is a real difference in slope. These are observational comparisons within one country's clinics, so they describe what happened, not what would happen if a patient moved between groups.