A new study has identified a glycosylated hemoglobin A1c (A1C) threshold of 5.9% in adults and 5.7% in children with cystic fibrosis (CF) that is associated with a higher risk of progression to cystic fibrosis-related diabetes (CFRD) and a lower probability of weight gain.

The study, published in Diabetes & Metabolism, found no difference in forced expiratory volume in one second (FEV1) according to A1C.

“First, we aimed to determine an A1C threshold associated with a higher risk of progression to CFRD in both an adult and a pediatric cohort,” the authors wrote. “Second, we wanted to determine A1C thresholds associated with the risk of adverse clinical change in key CF parameters such as BMI, FEV1, and in children, of linear growth.”

The research team assessed retrospective data on a cohort of 281 pediatric patients aged 10 to 17 years and prospective data on 308 adult patients with CF at two sites in Canada. Clinical data, including height, weight, body mass index, blood pressure, FEV1, A1C, and oral glucose tolerance test results were collected.

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The results revealed that a CF-specific threshold for A1C of almost 6%, lower than the traditional threshold of 6.5%, predicted a future risk of progression to CFRD as diagnosed by the results of oral glucose tolerance test. The authors noted the difference between the thresholds between adults and children in this study: Children who were 10 years old with higher than 5.5% A1C were at a greater risk of CFRD and adults with higher than 6.0% were at greater risk.

Furthermore, adults with an A1C higher than 6% did not gain weight during the study follow-up period, whereas those with less than 6% A1C did gain weight. In CF, being overweight and obesity is associated with better pulmonary outcomes.   

The authors concluded that A1C may be a simple and useful CFRD screening tool to identify those patients with CF who would benefit most from intensive nutritional management and support.


Potter K, Racine F, Bonhoure A, et al. A glycosylated hemoglobin A1c above 6% (42 mmol/mol) is associated with a high risk of developing cystic fibrosis-related diabetes and a lower probability of weight gain in both adults and children with cystic fibrosis. Diabetes Metab. Published online June 2, 2023. doi:10.1016/j.diabet.2023.101455