Airway glucose concentrations and effect on growth of respiratory pathogens in cystic fibrosis

BackgroundPulmonary decline accelerates in cystic fibrosis-related diabetes (CFRD) proportional to severity of glucose intolerance, but mechanisms are unclear. In people without CF, airway glucose (AG) concentrations are elevated when blood glucose (BG) ≥ 8 mmol L− 1 (airway threshold), and are associated with acquisition of respiratory infection.MethodsTo determine the relationship between BG and AG, 40 CF patients underwent paired BG and AG (nasal) measurements. Daily time with BG > airway threshold was compared in 10 CFRD, 10 CF patients with normal glucose tolerance (CF-NGT) and 10 healthy volunteers by continuous BG monitoring. The effect of glucose at airway concentrations on bacterial growth was determined in vitro by optical densitometry.ResultsAG was present more frequently (85%-vs.-19%, p < 0.0001) and at higher concentrations (0.5–3 mmol L− 1-vs.-0.5–1 mmol L− 1, p < 0.0001) when BG was ≥ 8 mmol L− 1-vs.-< 8 mmol L− 1. Daily time with BG ≥ 8 mmol L− 1 was CFRD (49 ± 25%), CF-NGT (6 ± 5%), healthy volunteers (1 ± 3%), p < 0.0001. Staphylococcus aureus growth increased at ≥ 0.5 mmol L− 1 (p = 0.006) and Pseudomonas aeruginosa growth above 1–4 mmol L− 1 glucose (p = 0.039).ConclusionsBG ≥ 8 mmol L− 1 predicted elevated AG concentrations in CF, at least in nasal secretions. CFRD patients spent ∼ 50% day with BG > airway threshold, implying persistently elevated AG concentrations. Further studies are required to determine whether elevated airway glucose concentrations contribute to accelerated pulmonary decline in CFRD.