Background: Oral glucose tolerance test (OGTT) is the screening test of choice for Cystic Fibrosis Related Diabetes (CFRD). HbA1C is considered unreliable in diagnosing CFRD because of increased cell turn over in children and adolescents with Cystic Fibrosis (CF).
Objective: To determine the validity of HbA1C as a predictive tool for future abnormal OGTT in CF.
Material & Methods: Data were collected on OGTTs and HbA1C (within 3 months of OGTT) in children and adolescents with CF, over the previous 15 years in a tertiary care centre. Sensitivity and specificity were calculated for HbA1C in predicting abnormal OGTT and for both HbA1C and OGTT in predicting insulin therapy.
Results: 150 OGTT (81 females) were included in this study. 77/150 (51%) had an abnormal OGTT with indeterminate (31/77) being the most common followed by impaired (26/77), CFRD (19/77) and CFRD with fasting hyperglycaemia (1/77). Sensitivity and specificity of HbA1C (>42 mmol/mol) to predict CFRD on OGTT were 68.4% and 84.3% respectively. HbA1C (>42 mmol/mol) was more sensitive (64.5%) than OGTT (43.4%) in predicting need for insulin therapy. Reducing HbA1C cut-off to > 40mmol/mol, increased sensitivity of HbA1C to detect CFRD on OGTT (78.9%) and need for insulin therapy (74.2%). Mean HbA1C increased with progressive phases of insulin dysregulation (mean HbA1C 38 (25-48) mmol/mol in normal OGTT, 40 (31-49) mmol/mol in indeterminate, 40 (30-49) mmol/mol in impaired and 48 (34-88) mmol/mol in CFRD). HbA1C rose from one year before an abnormal OGTT (mean rate of rise 1.7mmol/mol every 6 months). HbA1C was already in diabetic range 42 (37-49) mmol/mol 18 months before having CFRD on OGTT. HbA1C rose by 3 mmol/mol (from 37 to 40) a year before indeterminate and impaired OGTT.
Conclusion: HbA1C (>42mmol/mol) is more sensitive than OGTT in detecting CFRD patients who need insulin therapy. Increase in HbA1C by 3 mmol/mol in a year corelated with indeterminate and impaired OGTT.
22 Sep 2021 - 26 Sep 2021