Glycated Hemoglobin as a First-line Screening Test for Cystic Fibrosis‒Related Diabetes and Impaired Glucose Tolerance in Children With Cystic Fibrosis: A Validation Study.

Objectives: Our aims in this study were to document the screening rate for cystic fibrosis‒related diabetes (CFRD) in children followed at a cystic fibrosis (CF) clinic in Canada and to evaluate the accuracy of various glycated hemoglobin (A1C) cutoffs to screen for CFRD and impaired glucose tolerance (IGT) in a pediatric CF population.

Methods: The CFRD screening rate was calculated over a follow-up period of up to 8 years among children who attended the CF clinic between 1993 and 2018. Test performance of A1C at various thresholds ranging from 5.5% to 6.2% was compared with the oral glucose tolerance test (OGTT) as the reference method. Children with CF aged ≥10 years with an OGTT performed within 120 days of A1C measurement were included in the analysis.

Results: The overall CFRD screening rate was 53.0%. A total of 256 children were included for the A1C performance analysis, of whom 8.6% had an OGTT-confirmed CFRD diagnosis. An A1C threshold of 5.8% demonstrated an optimal balance between sensitivity (90.9%) and specificity (60.7%) for CFRD screening, leading to a potential reduction of 56.3% of the annual required OGTTs. A1C demonstrated poor accuracy for identifying children with IGT.

Conclusions: An A1C threshold ≥5.8% allows for identification of children requiring further CFRD investigations, which may reduce the clinical burden of children with CF without compromising the ability of early CFRD diagnosis.