Investigation of Screening Methods for Impaired Glucose Control in Children with Cystic Fibrosis

The oral glucose tolerance test (OGTT) used for the diagnosis of Cystic Fibrosis Related Diabetes (CFRD) is inconvenient and requires a great deal of patient cooperation. Other investigations such as measuring fasting glucose and glycosylated haemoglobin (HbA1c) concentrations, could offer several practical advantages over the OGTT for diabetic screening. To investigate the ability of these tests to detect impaired glucose control, 111 patients attending the Cystic Fibrosis Clinic at The National Children’s Hospital (Dublin, Ireland), were evaluated. All individuals had annual measurements of glucose and HbA1c, and those over 8 years of age underwent a complete OGTT every two years. Compared with the OGTT, HbA1c was highly specific (91%), and an elevated HbA1c usually indicated the presence of impaired glucose tolerance (sensitivity = 80%). A normal HbA1c did not, however, exclude a diagnosis of impaired glucose control. Predictive values (PPV = 47%, NPV = 98%) are in accordance with a useful diagnostic test, however they are affected by the low prevalence of impaired glucose control within this population. In short, it appears that HbA1c as measured in this study would properly identify the vast majority of subjects with impaired glucose control. TSMJ May 2000, vol 1, 7-11.