- Design
- Registry cohort, Poisson regression
- Population
- 4,477 people with cystic fibrosis-related diabetes in the UK; 31,311 person-years
- Primary outcome
- All-cause mortality by updated mean HbA1c
- Effect
- Rate ratio 1.41 (43–53), 1.66 (54–69), 1.93 (above 69) vs 42 mmol/mol or less
This UK Cystic Fibrosis Registry study followed 4,477 people with cystic fibrosis-related diabetes for 31,311 person-years, during which 758 died. It related an updated running mean HbA1c to mortality, adjusting for age, calendar year, sex, BMI, lung function and use of CFTR modulators.
Against HbA1c of 42 mmol/mol or less, adjusted mortality rate ratios were 1.41 at 43–53, 1.66 at 54–69 and 1.93 above 69 mmol/mol. The gradient began well below the thresholds often treated as acceptable in this condition.
This is observational, so it shows association, not that lowering HbA1c prevents deaths. Sicker patients with worse lung disease and nutrition may run higher glucose, and adjustment for lung function will not remove all of that. Still, it is a large, long dataset in a group where glycaemic targets are often relaxed because of other priorities.
- Check HbA1c regularly in cystic fibrosis-related diabetes; risk rose even in the 43–53 mmol/mol band.
- Treat cystic fibrosis-related diabetes as insulin-deficient diabetes; insulin remains the standard therapy.
- Coordinate glucose targets with the cystic fibrosis team, since nutrition goals often pull the other way.
- Remember HbA1c can under-read in cystic fibrosis; consider CGM where results and symptoms disagree.
Why it matters
It challenges the habit of tolerating high glucose in cystic fibrosis because other problems seem more pressing.
Don't overread it
This was observational — it cannot show that lowering HbA1c reduces deaths in cystic fibrosis.
The statistics, in plain English
A rate ratio of 1.93 means the death rate was about twice that of the lowest-HbA1c group after adjustment. The confidence intervals stay above 1 at every level, and the steady rise across bands makes chance unlikely, but confounding by illness severity is still possible.
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