OVERNIGHT URINARY URIC-ACID - CREATININE RATIO FOR DETECTION OF SLEEPHYPOXEMIA - VALIDATION-STUDY IN CHRONIC OBSTRUCTIVE PULMONARY-DISEASEAND OBSTRUCTIVE SLEEP-APNEA BEFORE AND AFTER TREATMENT WITH NASAL CONTINUOUS POSITIVE AIRWAY PRESSURE

During hypoxia ATP degradation to uric acid is increased in animal mod els and humans. To assess the reliability of an overnight increase in uric acid excretion as a marker of nocturnal hypoxemia, we selected 10 normal volunteers (7 males and 3 females), 29 COPD patients (26 males and 3 females), and 49 subjects with obstructive sleep apnea (OSA) (4 3 males and 6 females). The patients underwent standard polysomnograph y, which was repeated in 14 subjects with nasal continuous positive ai rway pressure (CPAP), and were subdivided into two groups: Group D inc luded desaturating subjects who spent at least 1 h at Sa(O2) < 90% and 15 min below 85%, and Group ND were nondesaturating subjects. The ove rnight change in the uric acid:creatinine ratio (DELTAUA:Cr) was negat ive in normal subjects (-27.5 +/- 9.1 [mean +/- SD]) and ND groups: -1 9.7 +/- 14.3 in COPD, -16.1 +/- 13.0 in OSA. In both COPD and OSA Grou p D, the ratio was usually positive: DELTAUA:Cr was 17.9 +/- 31.4 in G roup D COPD (p < 0.001 versus ND) and 10.1 +/- 30.7 in Group D OSA (p < 0.001 versus ND and versus normal subjects) despite 4 of 15 false ne gative results in COPD and 8 of 20 in OSA. CPAP effective treatment in duced a marked reduction ((p = 0.0024) in DELTAUA:Cr, leading to a neg ative value. We conclude that DELTAUA:Cr seems to be a promising index of significant nocturnal tissue hypoxia, with good specificity but po or sensitivity (about 30% false negative), which might be useful for t he long-term follow-up of outpatients on nasal CPAP with a positive ra tio at baseline.