CFRD affects 30% of all patients with cystic fibrosis (CF) by the age of twenty−five. Early diagnosis of CFRD is crucial to prevent the unnecessary deterioration of pulmonary function and nutritional status, both of which affect the patient's overall survival. The selective approach takes less patient time and is less expensive. If it is equally accurate it should be used routinely. The oral glucose tolerance test (OGTT) is the accepted method for detecting CFRD and the Cystic Fibrosis Trust guidelines recommend that patients with CF over the age of twelve years should be screened annually. Yung et al, questioned this approach and argued that performing OGTT on all CF patients is inconvenient and may not be cost effective, as patients have to starve overnight and need to spend an extra 2 hours in the hospital in addition to all the other annual review tests.