Serum uric acid and lactate levels among patients with obstructive sleep apnea syndrome: Which is a better marker of hypoxemia?

BACKGROUND AND OBJECTIVES: Tissue hypoxia due to repeated sleep apneas leads to increased serum levels of uric acid (UA) and lactate in patients with obstructive sleep apnea syndrome (OSAS). Studies on assessment of serum level of UA in patients of OSAS are available. However, research on simultaneous evaluation of levels of serum lactate and UA is lacking. DESIGN AND SETTING: Prospective, case-control study. PATIENTS AND METHODS: Forty patients suffering from OSAS, diagnosed by night polysomnography (PSG), were included in this study. Forty age- and sex-matched subjects in whom the presence of OSAS was ruled out by night PSG were included as healthy controls. Participants underwent a procedure for the measurement of serum UA and lactate before and after sleep. RESULTS: Both before and after sleep UA levels of patients with OSAS were found to be significantly higher (P=.001 and .002, respectively) as compared to UA levels of controls. A statistically significant (P=.02) overnight (after sleep) rise was observed in the serum lactate level of OSAS patients. The correlation between serum UA values and %TSTs (percentage of total sleep time spent) below 95% SaO2 (arterial oxygen saturation) (P=.02) was statistically significant. The correlation was positive with %TSTs below 90% SaO(2), whereas it was found negative with normal basal oxygen. No significant correlation was observed between serum UA and the AHI (apnea-hypopnea index). Polysomnographic variables failed to show significant correlation with serum UA on respective multiple regression models controlling for age, body mass index, and waist-hip ratio. However, plasma lactate levels after sleep correlated with %TSTs below 95% of SaO2 and AHI with P values of .02 and .01, respectively. CONCLUSIONS: Both serum UA and lactate were positively correlated with the degree of hypoxia in OSAS. The measurement of serum lactate level was a better marker of oxidative stress among patients with OSAS.