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

Background: Pulmonary 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)> or =8 mmol L(-1) (airway threshold), and are associated with acquisition of respiratory infection.

Methods: To 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.

Results: AG 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 > or =8 mmol L(-1)-vs.-<8 mmol L(-1). Daily time with BG> or =8 mmol L(-1) was CFRD (49+/-25%), CF-NGT (6+/-5%), healthy volunteers (1+/-3%), p<0.0001. Staphylococcus aureus growth increased at > or =0.5 mmol L(-1) (p=0.006) and Pseudomonas aeruginosa growth above 1-4 mmol L(-1) glucose (p=0.039).

Conclusions: BG> or =8 mmol L(-1) predicted elevated AG concentrations in CF, at least in nasal secretions. CFRD patients spent approximately 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.