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

HbA 1c is recommended for monitoring glycaemic control in people with cystic fibrosis-related diabetes (CFRD). However the relationship between HbA 1c and mean plasma glucose concentration (MPG) has not been established in CFRD, as in other forms of diabetes mellitus. 20 people (13 male, 29.7 ± 8.8 years, 10 CFRD) with cystic fibrosis (CF) underwent HbA 1c measurement and 48 h continuous glucose monitoring for estimation of MPG. The relationship between HbA 1c and MPG was established and compared to the reported relationship for type 1 diabetes. HbA 1c was strongly correlated with MPG ( R 2 = 0.888, p < 0.0001) in CF. The relationship of MPG to HbA 1c was described by the equation MPG = (1.47 × HbA 1c) − 1.15, giving a 1.47 mmol L − 1 change in MPG per 1% change in HbA 1c. This equation predicts that MPG in people with CF and HbA 1c < 7.0% will be similar to MPG in people with type 1 diabetes who achieve the same HbA 1c target. These results imply that HbA 1c < 7.0% will predict good blood glucose control in CF as in type 1 diabetes. However, although HbA 1c predicts complications in type 1 diabetes, further studies are required to establish the relationship between HbA 1c and diabetic complications in people with CFRD.