Introduction An association between OSA and asthma has been demonstrated. The exact prevalence in the SDTA population is unknown.

Aim To determine the prevalence and predictors of OSA in the SDTA population

Methods All patients who attended a severe asthma regional centre between January 2013 and August 2016 with confirmed SDTA were asked to participate. All patients without a pre-existing OSA diagnosis had an overnight limited-channel sleep study. Patients underwent bioelectrical impedance measurements and completed the Epworth Sleepiness Score (ESS).

Results 72 patients consented and were included in the analysis. 69.4% (n = 50) had OSA. 33.3% (n = 24) had a pre-existing diagnosis of OSA and 79% (n = 19) of this group were receiving Continuous Positive Airway Pressure (CPAP). 36% (n = 26) had a new diagnosis of OSA. 31% (n = 22) had OSA excluded with a negative sleep study. Mild OSA (Apnoea Hypopnoea Index(AHI) ≥5–14.9) = 31.9% (n = 23), moderate OSA (AHI ≥ 15–29.9) = 16.7% (n = 12), severe OSA (AHI ≥ 30) = 4.2% (n = 3). AHI was unknown for 16.6% (n = 12) with pre-existing OSA receiving CPAP from a specialist centre.

The mean age was 47.7 years (18–73) and 72.2% (n = 52) were female. Mean Body Mass Index (BMI) was 32 (18.6–65.7). ESS was higher in the OSA group compared to the no-OSA group (11.0 vs 8.7, p = 0.091). The OSA group had significantly higher BMI (34.7 ± 8.00 vs 28.8 ± 9.62, p = 0.007) and body fat percentage (38.7 ± 12.37 vs 28.3 ± 14.03 fat%, p = 0.003) compared to the no-OSA group. The OSA group had a significantly higher incidence of hypercholesterolaemia compared to the no-OSA group (32.6% vs 8%, p = 0.0239). There was a higher incidence of diabetes (18.6% vs 8%, p = 0.0932), hypertension (27.9% vs 16%, p = 0.1643) and gastro-oesophageal reflux (60.5% vs 54.2%, p = 0.6189) in the OSA group. Blood eosinophil levels were significantly lower in the OSA group compared with the no-OSA group (0.23 ± 0.18 vs 0.39 ± 0.29 x10^9/L, p = 0.004).

Conclusion A significant prevalence of OSA was noted in this SDTA population. BMI, percentage body fat and hypercholesterolaemia were the strongest predictors of OSA. Patients with OSA had significantly lower blood eosinophil levels when compared to the no-OSA group. Alternatives to eosinophilic inflammation as a driver for severe/difficult to treat asthma should always be considered.