Prevalence of hyperuricemia in patients with obstructive sleep apnea from the Mallorca cohort

Abstract

Intermittent hypoxia increases purine metabolism and uric acid (UA) production. The Metabolic Syndrome is also associated with hyperuricemia, leading some authors to propose that UA may be used as a marker of increased cardiovascular risk. We analyzed data from 525 patients studied by polysomnography in the Sleep Laboratory of the University Hospital, Palma de Mallorca, Spain to assess: 1) prevalence of hyperuricemia, defined as UA values ≥8 mg/dL; 2) the relationships between UA and both OSA severity and metabolic abnormalities. Mean UA in the sample was 6.3±2.6 mg/dL, and UA was increased in 68 patients (prevalence 13%). Compared to patients with normal UA, hyperuricemic patients were older (age±SD 55.3±12.7 vs 50.6±12.7 yr, p=0.005), heavier (BMI 32.9±5.3 vs 30.7±6.3, p=0.007), had more severe OSA (AHI: 56.4±27.0 vs 41.6±27.2, p<0.0001; lowest SaO2: 76-2±10.1 vs 81.4±9.1%, p<0.0001), higher C-reactive protein level (5.2±4.4 vs 3.6±4.8 mg/L, p<0.001), higher creatinine (1.07±0.30 vs 0.93±0.27 mg/dL, p=0.0001), higher insulin resistance (HOMA Index 5.76±3.70 vs 3.52±2.85, p<0.0001) and higher Metabolic Index (3.1±1.0 vs 2.2±1.4, p<0.0001). Weak univariate relationships were found between UA and BMI, AHI, lowest and mean SaO2,creatinine, HOMA ln, and Metabolic Index, explaining each 5 to 9% of UA variability. Stepwise multiple regression identified the following independent correlates of UA (R²=0.23, R=0.48, p<0.0001): gender, creatinine, diuretic treatment, Metabolic Index, and mean SaO2. Results were unchanged after exclusion of 40 diabetic patients. These preliminary data suggest that both intermittent hypoxia and metabolic abnormalities affect UA levels in untreated OSA patients.