Agreement Between HbA1C and Continuous Glucose Monitoring-Derived Glycemic Metrics in Adults With Cystic Fibrosis Related Diabetes.

OBJECTIVE

Cystic fibrosis related diabetes (CFRD) is a prevalent complication of cystic fibrosis that requires accurate assessment of glycemic control to guide management. Whether HbA1C reliably reflects mean glycemia in adults with CFRD, particularly in the context of continuous glucose monitoring (CGM) adoption and modern cystic fibrosis transmembrane conductance regulator modulator therapy, remains uncertain.

METHODS

This retrospective cross-sectional study, conducted at a single CF center, evaluated adults with confirmed CFRD who had a laboratory HbA1C paired with at least 30 days of CGM data with ≥70% active sensor time during the preceding 30-90 days. Individuals with conditions that affect HbA1C reliability, such as anemia, advanced chronic kidney disease, or pregnancy, were excluded.

RESULTS

Forty-nine adults met the inclusion criteria (mean age 43.9 ± 11.6 years; 69.4% male), with high CGM adherence (median sensor active time of 97%). Their mean HbA1C was 7.3% ± 1.1% (56 ± 12 mmol/mol), while mean Glucose Management Indicator (GMI) and mean sensor glucose were 7.6% ± 1.0% (60 ± 11 mmol/mol) and 178.6 ± 40.3 mg/dL (9.9 ± 2.2 mmol/L), respectively. HbA1C demonstrated strong correlations with GMI (r = 0.90; P< .0001) and mean sensor glucose (r = 0.90; P< .0001). Bland-Altman analysis showed a mean bias of +0.30% (GMI-HbA1C), with 95% limits of agreement from -0.65% to +1.25% and no proportional bias across the glycemic range.

CONCLUSION

These findings indicate that HbA1C closely reflects CGM-derived mean glycemia in adults with established CFRD. While CGM metrics provide complementary clinical information, integrating both measures may improve monitoring and therapeutic decision-making in CFRD care.