Serum levels of NGAL and cystatin C as markers of early kidney dysfunction in patients with obstructive sleep apnea syndrome

Abstract

Purpose: Obstructive sleep apnea syndrome (OSAS) has been recently proposed as an independent risk factor for chronic kidney disease. Cystatin C (Cyst C) and neutrophil gelatinase-associated lipocalin (NGAL) are novel biomarkers for the earlier detection of latent kidney disease. The aim of the study was to assess serum Cyst C and NGAL levels in otherwise healthy OSAS patients and to explore possible associations with sleep parameters.

Methods: Consecutive subjects (n = 96, 79.2% males), without known comorbidities, with symptoms suggestive of OSAS were included. All of them underwent polysomnography (PSG) and blood examination for the measurement of serum Cyst C and NGAL levels.

Results: Based on apnea-hypopnea index (AHI), subjects were classified into two groups: 32 controls and 64 OSAS patients, with no significant differences in terms of age (50.1 ± 11.7 vs 51 ± 12.2 years, p = 0.747) and BMI (33.9 ± 8.8 vs 35.9 ± 13.1 kg/m², p = 0.449). Serum Cyst C and NGAL mean levels were higher in OSAS patients compared to those in controls (1155.2 ± 319.3 vs 966.8 ± 173 ng/ml, p = 0.001, and 43.7 ± 23.2 vs 35.6 ± 13.8 ng/ml, p = 0.035, respectively). After adjustment for age and BMI in OSAS patients, serum NGAL levels were associated with AHI (β = 0.341, p = 0.015) and minimum oxyhemoglobin saturation during sleep (β = - 0.275, p = 0.032), while serum Cyst C levels were associated with percentage of time with oxyhemoglobin saturation < 90% (β = 0.270, p = 0.043), average (β = - 0.308, p = 0.018), and minimum (β = - 0.410, p = 0.001) oxyhemoglobin saturation during sleep.

Conclusions: Higher risk for latent kidney disease in otherwise healthy OSAS patients is indicated. Sleep hypoxia seems to be a significant contributor in the pathogenetic process of renal dysfunction in OSAS.

Keywords: Cystatin C; Kidney dysfunction; Kidney injury; NGAL; Obstructive sleep apnea syndrome.