title: Disposition index identifies defective beta-cell function in cystic fibrosis subjects with normal glucose tolerance.
abstract: BACKGROUND
  In non-cystic fibrosis (CF) subjects, the disposition index (DI) is a strong predictor of the development of type 2 diabetes. CF subjects are at high risk of diabetes. We hypothesized that DI would be reduced in CF patients with normal glucose tolerance (NGT), indicating β-cell dysfunction, and DI would worsen with progression from CF with NGT to CF-related diabetes (CFRD).
  
  
  METHODS
  This was a cross-sectional study in 39 CF patients and 21 healthy controls (Con) who underwent oral glucose tolerance test (OGTT). Insulin sensitivity was estimated as (1/fasting insulin) and insulin secretion as (∆insulin 0-30min/∆glucose 0-30min). DI was calculated as (insulin sensitivity)×(insulin secretion).
  
  
  RESULTS
  Among CF subjects, 14 had NGT, 20 had prediabetes and 5 had CFRD. Among the controls, 14 had NGT and 7 had prediabetes. DI was significantly lower in CF-NGT compared to Con-NGT (p=0.0035). DI was also lower in CFRD compared to CF-NGT (p=0.025). There were no significant relationships in the CF groups between DI and age, BMI, percent body fat or FEV1.
  
  
  CONCLUSIONS
  β-Cell function as measured by DI is reduced in CF patients compared to non-CF controls-even in CF-NGT-and is decreased further in CF patients with diabetes. If DI proves to be a predictor of the development of CFRD in larger studies, then it could be used to identify CF patients who are at particularly high risk, allowing early interventions aimed to delay or prevent CFRD.
authors.affiliation: Division of Endocrinology and Diabetes, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA. Electronic address: linamerjaneh@msn.com.
authors.forename: L
authors.initials: L
authors.lastname: Merjaneh
authors.affiliation: Department of Biostatistics and Bioinformatics, Rollins School of Public Health, Emory University, Atlanta, GA, USA. Electronic address: Qing.he@emory.edu.
authors.forename: Q
authors.initials: Q
authors.lastname: He
authors.affiliation: Department of Biostatistics and Bioinformatics, Rollins School of Public Health, Emory University, Atlanta, GA, USA. Electronic address: qlong@emory.edu.
authors.forename: Q
authors.initials: Q
authors.lastname: Long
authors.affiliation: Atlanta VA Medical Center, Decatur, GA, USA; Division of Endocrinology and Diabetes, Department of Medicine, Emory University School of Medicine, Atlanta, GA, USA. Electronic address: medlsp@emory.edu.
authors.forename: L S
authors.initials: LS
authors.lastname: Phillips
authors.affiliation: Division of Pulmonary, Allergy/Immunology, Cystic Fibrosis, and Sleep, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA. Electronic address: astecen@emory.edu.
authors.forename: A A
authors.initials: AA
authors.lastname: Stecenko
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D015897:Comorbidity; D003430:Cross-Sectional Studies; D003550:Cystic Fibrosis / Q000097:blood* / Q000175:diagnosis / Q000453:epidemiology; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology; D018450:Disease Progression; D005260:Female; D018149:Glucose Intolerance / Q000503:physiopathology; D005951:Glucose Tolerance Test; D006801:Humans; D015994:Incidence; D007328:Insulin / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D008297:Male; D011236:Prediabetic State / Q000175:diagnosis* / Q000453:epidemiology; D011379:Prognosis; D012016:Reference Values; D018570:Risk Assessment; D012737:Sex Factors; D018709:Statistics, Nonparametric; D055815:Young Adult
chemical_list: D007328:Insulin
keywords: Beta-cell function; Cystic fibrosis; Diabetes; OGTT