Objective: Cystic fibrosis-related diabetes (CFRD) is associated with adverse clinical outcomes and should be screened for by an annual oral glucose tolerance test (OGTT). Since pathophysiologic studies have mainly been performed in a pediatric/adolescent, nontransplanted collective, we aimed to assess parameters of insulin secretion and sensitivity in adult cystic fibrosis (CF) patients after lung transplantation (LT).
Methods: Twelve adult CF patients after LT without known diabetes (33.3 ± 11.5 years; body mass index [BMI] 21.5 ± 3.3 kg/m2) and 8 control subjects matched by age (36.0 ± 6.6 years; P>.05), BMI (22.3 ± 1.5 kg/m2; P>.05), and gender (CON group) underwent a 3-hour OGTT with glucose, insulin, and C-peptide measurements. Parameters of insulin secretion and sensitivity as well as lipid profiles were assessed.
Results: In the CF group, 4 patients were diagnosed with overt diabetes (CFRD) compared to CF patients without diabetes (CF-noDM), of whom 6 had indeterminate glycemia with 1-h glucose values >200 mg/dL. The insulin peak after glucose load occurred after 30 minutes in CON, after 90 minutes in CF-noDM, and was missing in CFRD. Insulin sensitivity was comparable between the groups. Beta-cell glucose sensitivity was markedly reduced in CFRD (10.7 ± 5.8 pmol/min*m2*mM), higher in CF-noDM (39.9 ± 23.4 pmol/min*m2*mM), but still significantly lower compared to CON (108.3 ± 53.9 pmol/min*m2*mM; P = .0008). CFRD patients exhibited increased triglyceride levels and decreased high-density lipoprotein levels.
Conclusion: Adult CF patients after LT have profound disturbances in glucose metabolism, with a high rate of undetected diabetes and markedly delayed insulin secretion. Curbed beta-cell glucose sensitivity rather than insulin resistance explains postprandial hyperglycemia and is accompanied by abnormalities in lipid metabolism.
Abbreviations: AUC = area under the curve; BMI = body mass index; CF = cystic fibrosis; CFRD = cystic fibrosis-related diabetes; CFTR = cystic fibrosis transmembrane-conductance regulator; CF-TX = cystic fibrosis patients who underwent lung transplantation; CGM = continuous glucose monitoring; HbA1c = glycated hemoglobin; HDL = high-density lipoprotein; INDET = indeterminate glycemia; LDL = low-density lipoprotein; LT = lung transplantation; OGIS = oral glucose sensitivity index; OGTT = oral glucose tolerance test; QUICKI = quantitative insulin sensitivity check index.