Glomerular filtration rate in patients with obstructive sleep apnea: the influence of cystatin-C-based estimations and comorbidity

BACKGROUND: Recent studies indicate that chronic kidney disease (CKD) is a comorbidity in patients with obstructive sleep apnea (OSA). We hypothesized that the use of the classical muscle-dependent, creatinine-based equation to estimate glomerular filtration rate (GFR) in patients with OSA may be inaccurate due to the extreme body mass index (BMI) of some patients. The aim of this study was to establish the role of cystatin-C-based estimation of GFR for the detection of CKD in patients with OSA and typical comorbidities. METHODS: Two hundred and forty consecutive patients with newly diagnosed OSA were enrolled into this cross-sectional study. In all patients estimated GFR (eGFR) was calculated with chronic kidney disease-epidemiology collaboration group (CKD-EPI) equations using creatinine and cystatin-C. All patients were examined for comorbidities. RESULTS: In obese patients with OSA significant differences between GFR estimations based on creatinine and cystatin were found: eGFR based on muscle-dependent creatinine measurement was significantly higher than the muscle-independent eGFR based on cystatin-C measurement. CONCLUSIONS: GFR can be routinely screened for using creatinine-based estimations (eGFRcreat). In a selected group of patients with OSA with BMI over 30 kg/m(2) the addition of cystatin-C for assessment of eGFR is suggested.