Abstract
BackgroundSerum cystatin C is a sensitive indicator for early renal impairment in patients with obstructive sleep apnea (OSA). In patients with OSA without known chronic kidney disease (CKD), serum cystatin C was found to be elevated, indicating latent renal disease, which may be caused by recurrent episodes of hypoxemia and reoxygenation that trigger inflammatory process.ObjectiveTo evaluate serum levels of cystatin C in otherwise healthy patients with OSA to predict the future risk of latent renal impairment in these patients.Patients and methodsA total of 30 patients were classified into two groups: group I included 10 healthy controls, and group II included 20 patients with OSA.The following were done: full history taking, clinical examination, pulmonary function tests, subjective evaluation of daytime sleepiness using the Epworth Sleepiness Scale, and overnight polysomnography. Finally, serum cystatin C levels at the end of polysomnography and glomerular filtration rate was calculated using modification of diet in renal disease formula and CKD-Epidemiology Collaboration cystatin equation.ResultsIn patients with OSA, the mean level of serum cystatin C was statistically significantly higher than that in controls. These higher levels were sex, age, and BMI independently. Moreover, serum levels of cystatin C in patients with OSA were significantly correlated with OSA severity (apnea-hypopnea index) and degree of nocturnal hypoxia through positive correlation with total sleep time less than 90%, total sleep time less than 80%, and respiratory disturbance index and negative correlation with average SPO2%, lowest SPO2%, and estimated glomerular filtration rate by CKD-Epidemiology Collaboration cystatin equation.ConclusionsHigher serum levels of cystatin C were detected in patients with OSA without known comorbidities, which indicates that these patients are at a higher risk of developing CKD. Intermittent hypoxia seems to have the main role in the progression of this process.
Highlights
Obstructive sleep apnea (OSA) is characterized by recurrent attacks of either partial or complete upper airway collapse, resulting in hypopnea or apnea during sleep [1]
Cystatin C, a protein with a low molecular weight, is an inhibitor of lysosomal cysteine protease. It is mainly used as a biomarker for kidney function, as cystatin C is filtered by glomeruli and reabsorbed and catabolized in the proximal convoluted tubules, but it is not secreted by the tubules [4]
This work aimed at evaluation of serum levels of cystatin C in otherwise healthy patients with OSA to predict the future risk of latent renal impairment in these patients
Summary
Obstructive sleep apnea (OSA) is characterized by recurrent attacks of either partial or complete upper airway collapse, resulting in hypopnea or apnea during sleep [1]. Cystatin C, a protein with a low molecular weight, is an inhibitor of lysosomal cysteine protease. In contrast to serum creatinine, cystatin C is not influenced by either muscle mass, age, or sex. It is a more sensitive indicator of mild and early kidney impairment and is a faster and a better estimate of glomerular filtration rate (GFR) than serum creatinine [5]. Serum cystatin C is a sensitive indicator for early renal impairment in patients with obstructive sleep apnea (OSA). In patients with OSA without known chronic kidney disease (CKD), serum cystatin C was found to be elevated, indicating latent renal disease, which may be caused by recurrent episodes of hypoxemia and reoxygenation that trigger inflammatory process
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