In the CF-IDEA Trial, subjects with CF aged >=5 years with early glucose abnormalities (CFID1 or 2) will be randomised to once-daily insulin detemir (Levemir) for 12 months, or to observation only. We aim to determine whether starting insulin earlier than current practice will prevent decline in weight and lung function, reduce frequency of hospitalisation, improve quality of life, and slow progression through CFID categories.