In patients undergoing polysomnography (PSG) for suspected obstructive sleep apnea (OSA), the urinary N-acetyl-β-D-glucosaminidase creatinine ratio (uNAG/Cr) increased as the 3% oxygen desaturation index (ODI) increased, according to study findings published in Sleep Medicine.
The rate of chronic kidney disease, which is associated with renal tubular injury, is high among those with OSA; however, the effect of OSA-induced chronic intermittent hypoxia (IH) on the renal tubules remains to be explored. Investigators therefore conducted a retrospective, observational, single-center, cohort study to evaluate the association between renal tubular injury and chronic IH, as well as the effect of CPAP on renal tubular injury. The participants were adults who underwent PSG at a hospital in Niigata, Japan, between January 2006 and March 2016.
The cohort was categorized into 4 groups based on their degree of 3% ODI (group 0: 3% ODI, less than 5; group 1: 3% ODI, 5 to 14; group 2: 3% ODI, 15 to 29; and group 3: 3% ODI, 30 or more).
A total of 197 patients (mean [SD] age, 50.74 [16.21] years; 130 male) were enrolled in the initial analysis, including 34 patients with apnea-hypopnea index (AHI) less than 5 events per hour; 46 patients were included in the secondary PSG analysis (mean follow-up: 396.8 [274.8] days). The participants were grouped as follows: group 0, n=41; group 1, n=44; group 2, n=49; and group 3, n=63.
As the severity of 3% ODI increased, uNAG/Cr, urinary B2M-creatinine ratio, blood pressure (BP), hemoglobin A1c (HbA1c), and high-sensitivity C-reactive protein (hsCRP) also gradually increased.
A subgroup analysis included patients with OSA (AHI ≥5 events/hour, n=163). When the severity of 3% ODI increased, uNAG/Cr, urinary B2M/Cr, BP, HbA1c, and hsCRP also increased gradually (uNAG/Cr, P =.014; urinary B2M/Cr, P =.005; systolic BP, P <.001; diastolic BP, P <.001; HbA1c, P =.002; and hsCRP, P <.001).
Multiple linear regression models showed that age and 3% ODI were significantly associated with uNAG/Cr.
The participants with OSA aged 55 and younger (n=82) were further categorized for subgroup analysis into 2 groups, for severe and less-severe 3% ODI, using 40 events per hour 3% ODI as the cutoff. Those aged 55 and older with severe 3% ODI had significantly higher uNAG/Cr (P =.014), urine albumin-creatinine ratio (P =.015), and increased prevalence of major comorbidities compared with the less-severe group.
Limitations include the single-center design, which limits the generalizability of the findings across geographic regions. Also, the observation period between diagnostic PSG and follow-up PSG was about 1 year, and some patients could not achieve good adherence for CPAP treatment in the secondary analysis. Furthermore, although 3% ODI was associated with uNAG/Cr, the effect of age could not be excluded.
“Our results suggest that chronic IH induces renal tubular and tubulointerstitial injury, and early induction of CPAP therapy in patients with OSA could ameliorate further injury and the course towards end-stage renal disease (ESRD),” the study authors concluded. Given the enormous burden posed by renal replacement therapy, “a better understanding of the potential role of OSA-induced chronic IH in renal tubular and tubulointerstitial injury may be important for both clinicians and health policymakers,” the researchers added.
Moriya R, Hokari S, Ohshima Y, et al. Continuous positive airway pressure treatment reduces renal tubular damage in patients with obstructive sleep apnea: a retrospective single-center cohort study. Sleep Med. Published online April 5, 2023. doi:10.1016/j.sleep.2023.03.028