Cystic Fibrosis-Related Diabetes Screening in Adults: A Gap Analysis and Evaluation of Accuracy of Glycated Hemoglobin Levels.

Abstract

We sought to identify the gap in cystic fibrosis-related diabetes (CFRD) screening by means of an oral glucose tolerance test (OGTT) in our tertiary care clinic. Our second aim was to identify the glycated hemoglobin level (A1C) threshold that optimizes sensitivity and specificity for predicting CFRD and impaired glucose tolerance. This retrospective study used data housed in the Toronto cystic fibrosis (CF) database. The study population included all adult (≥18 years of age) patients seen in the CF clinic between January 1, 2008, and December 31, 2015. Descriptive statistics were used for the OGTT gap analysis; the CFRD screening rate was calculated on an annual basis as the proportion of eligible patients who received OGTTs. Sensitivity and specificity were calculated using OGTTs as the reference standard and A1C levels as the index test on a sample size of 320 patients. On average, 48.5% of eligible individuals were screened each year for CFRD by OGTTs. A1C thresholds of 5.5% had a sensitivity of 91.8% (75%) and a specificity of 34.1% (33.4%) for the diagnosis of CFRD (and impaired glucose tolerance), respectively. Of the 229 patients with A1C levels <5.5%, 5 test results (2.2%) had OGTTs indicative of CFRD. The rate of CFRD screening is suboptimal. An alternative screening algorithm using an A1C threshold of 5.5% has the potential to reduce the requirement for OGTTs by 36.7%. A1C levels cannot be used to identify impaired glucose tolerance.