[Blood uric acid levels in patients with sleep-disordered breathing]

Recurrent hypoxia associated with sleep apnea-hypopnea syndrome (SAHS) leads to an increase in the degradation of adenosine triphosphatase to xanthine and, secondarily, to an increase in uric acid concentrations. The aim of the present study was to determine whether there is a correlation between uric acid levels in peripheral blood and sleep-disordered breathing, independently of known confounding factors.

We carried out a retrospective cross-sectional study of 1135 patients evaluated for suspected SAHS. For all patients, a medical history was taken using a standardized protocol. In addition, biochemical analysis of venous blood and an overnight sleep study (with either conventional polysomnography or home monitoring) were carried out.

The mean (SD) concentration of uric acid was 6.31 (1.5) mg/dL, and 36% of patients had concentrations above established normal values for their sex. We found a significant correlation between uric acid levels and some sleep study parameters (number of respiratory events, number of desaturations, or the cumulative percentage of time with oxygen saturation less than 90%). Those patients with more respiratory events (apnea-hypopnea index or respiratory event index >or= 30) had higher uric acid levels than those with mild or no SAHS. However, this difference was not apparent in the univariate analysis of variance, in which body mass index and cholesterol and triglyceride levels were considered confounding factors.

Uric acid levels are positively correlated with the number of obstructive respiratory episodes and oxygen desaturations during sleep, but this correlation seems to be influenced by other factors, such as obesity.