Relationship between glycosylated haemoglobin and mean plasma glucose concentration in cystic fibrosis

BackgroundHbA1c is recommended for monitoring glycaemic control in people with cystic fibrosis-related diabetes (CFRD). However the relationship between HbA1c and mean plasma glucose concentration (MPG) has not been established in CFRD, as in other forms of diabetes mellitus.Methods20 people (13 male, 29.7 ± 8.8 years, 10 CFRD) with cystic fibrosis (CF) underwent HbA1c measurement and 48 h continuous glucose monitoring for estimation of MPG. The relationship between HbA1c and MPG was established and compared to the reported relationship for type 1 diabetes.ResultsHbA1c was strongly correlated with MPG (R2 = 0.888, p < 0.0001) in CF. The relationship of MPG to HbA1c was described by the equation MPG = (1.47 × HbA1c) − 1.15, giving a 1.47 mmol L− 1 change in MPG per 1% change in HbA1c. This equation predicts that MPG in people with CF and HbA1c < 7.0% will be similar to MPG in people with type 1 diabetes who achieve the same HbA1c target.ConclusionsThese results imply that HbA1c < 7.0% will predict good blood glucose control in CF as in type 1 diabetes. However, although HbA1c predicts complications in type 1 diabetes, further studies are required to establish the relationship between HbA1c and diabetic complications in people with CFRD.