Prevalence of chronic kidney disease in patients with suspected sleep apnoea

BACKGROUND: Little is known about the epidemiology of chronic kidney disease (CKD) in patients with suspected sleep apnoea (SA). METHODS: Glomerular filtration rate (eGFR) was calculated in consecutive patients referred for full-night observed in-hospital polysomnography. SA was defined as the respiratory disturbance index (RDI) > 5. RESULTS: One hundred and fifty-eight patients were studied. The age (mean +/- SD) was 61.2 +/- 12.7 years, body mass index 29.5 +/- 5.9 kg/m(2) and eGFR 86.1 +/- 21.7 mL/min/1.73 m(2). SA was present in 133 patients (85%). The eGFR was 94.6 7 mL/min/1.73 m(2) in patients without SA and 84.5 7 mL/min/1.73 m(2) in patients with SA [mean difference (95% confidence interval) 10.0 (0.6-19.4) mL/min/1.73 m(2); P = 0.037]. Seventy patients had eGFR > or = 90 mL/min/1.73 m(2) (group 1), and 70 patients had between 60 and 89 mL/min/1.73 m(2) (group 2), and 18 patients had 30-59 mL/min/1.73 m(2) (CKD 3). Although the prevalence of SA did not differ among the groups (group 1: 80%; group 2: 86%; CKD 3: 94%), the number of central sleep apnoeas (CSA) per hour was 5.9 +/- 12.2 in CKD 3, six times greater compared to patients with eGFR > or = 60 mL/min/1.73 m(2) (1.0 +/- 2.1; P = 0.01). The prevalence of obstructive SA did not differ between the groups. After adjustment for age, gender, BMI, hypertension, diabetes mellitus and smoking status, CKD 3 (P = 0.0004) and New York Heart Association class > or =3 (P = 0.0001) remained predictive of CSA events per hour. CONCLUSIONS: eGFR is reduced in patients with SA, particularly in those with episodes of CSA.